Since I don't care if anyone "copies" me anymore, I'll try to answer the questions in this thread.
First off:
"Wtf kind of differential do you have?"
I have a Tochigi Fugi Sangyo 2-way clutch type differential AKA THE MAZDASPEED PROTEGE OEM UNIT. You can buy this from your Mazdaspeed dealership. I called it the Tochigi Fugi Sangyo b/c thats what it is.....plus its fun to throw people off when you don't want everyone "copying" your setup.
"How was the installation? Any difficulties?"
Yes there are a few things to know, but if you researched first you'd know all of these. FIrst off the MSP does NOT have a speedometer ring on the differential. IT uses its ABS sensors to tell the speedo what speed the car is going (aka the axle's speed). Since the LSD doesn't have a plastic speedometer ring, you need to buy one for your speedo gear. Get it new from the mazda dealership for MX-3 or Probe GT.
You also need a pair of new bearings for the LSD as it does not come with these out of the box. You also should order the lil pin thingy that goes inside the diff and I think there is one other minor part you need (a lock nut for the primary & secondary gearshafts).
You may need to have the diff slightly machined where the speedo ring presses on, as the diff is sprayed with a textured paint or coating that kinda makes it unsmooth. You might be able to sand this off w/a dremel or something, but the machine shop you take the diff to to have the bearings pressed on should have the tools to do this anyways.
ANOTHER NOTE: If you read about this diff on msprotege.com forums you'll see people b----ing about how its a weak pos and breaks. This is true. If you are pushing more than a lightly modded KLZE you should DEFINITELY have the differential welded to the ring gear before installing. Since its out anyways, might as well right? The pos rivets that teh diff is held together with apparently are crap and break if you put down too much power. So a safeguard is to weld the diff to the ring gear ESP if you are NAWzzing or running FI.
"How is the Differential? Does it kick a--?"
I dunno, I don't drive like an a-- enough to determine if it helps my drag launches....add to the fact my current tires are 205/60 Falken ZEIX 512's on my stock 15's and POS Kumho 711's on my 16" Rota's. I plan on getting the new designed Azenis on my Rota's when the proper size comes out in August but until then I won't have any good tires to really test this thing out w/.
I have, however driven on some windy roads, but I've yet to auto-x with the diff yet. It DOES help in the corners immensely. If you are pushing the mofo to its limits in the corners you will feel the car pull hard as fock out of the corner if you are flooring it (and revving higher as the KLZE powerband sux down low). I also drove it quite a bit in the snow, it helped quite a bit.
I don't know how to test the deceleration aspects of the diff (braking), plus my brakes SUCK right now and I"m in the process of completely overhauling every component in the system so until then I don't know if it kicks a-- in that deparment.
"How much is the differential?"
I paid $320 (you read right) for mine. I paid like 28 dollars for both of the bearings, 8 dollars for the speedo ring and like 9 dolars per each of the lock nuts. ALl in all I paid like $420 shipped total for everything. Since most ppl here don't have a Mazda account like I do, you'll have to pay retail which is approx $580 for the unit, possibly as much as 25 PER bearing (u need two) and 12 for the locknuts and speedo rings. All in all, maybe 700 total for everything.
Machine work costed me $40 for the pressing of the bearings & speedo ring and My buddy welded the diff for free using a MIG (i think it was) welder. Dunno how much welding costs but I don't think it will cost much to have it welded if you take it to an exhaust shop or something.
"What other things should I know?"
I'm not 100% sure on this but I think you DEFINITELY NEED 4.11 final drive gears to fit this differential. Your stock diff is a 4.39 final drive, this diff is a 4.105 (4.11). I tried fitting my stock gears w/this diff in and they didn't turn, they jammed when I tried to turn the primary or secondary shafts.
Luckily I'm a bastard (as usual) and found a 1999 Ford ZX2 SR at the junkyard, the same one I got my current suspension from. I lucked out hardcore b/c someone pulled the Zetec engine and left the transmission sitting on the ground. I bought the transmission for $75 pre-pulled, took it home, opened it up.
Guys on PT have stated in the past that the 97+ Ford Escorts (which all have G-series gear boxes) had better gears and synchronizers. The gears are cut at better angles & the sychros are made of brass instead of copper which corrodes if you use the wrong fluid (fluid w/sulfur eats copper). So I put those in and they fit perfectly. I messed w/the 5th gear too and used my old one in combination with a differnet "idler" gear for the 5th gear and whaddya know! Now my 5th is WAY TALLER than it ever was before. I think I effectively reduced it to the .69 from .80 based on some calcuations I made but hell if I know. I rev at 3300rpm at 70mph now which is at least 300 rpm less than I did with my stock gearbox.
ADDITIONAL INFORMATION:
FYI for those who are out of the know....the list below details the G-series mazda gear box:
Cars with 4.39 final drive:
-92-96 MX-3 GS with 1.8 V6
-93-97 Ford Probe GT
Cars with 4.11 Final drive:
-90-94 Mazda Protege LX (1.8 dohc)
-95 Protege ES
-93-97 Mazda 626 and MX-6 (both 4cyl and 6cyl
-98-02 Mazda 626 (all models)
-01-03.5 Protege (all with 2.0 engines)
-91-94 Mercury Capri (all) note, these all have a cable operated clutch (which doesn't really matter if ur just taking the gears)
-91-96 Ford Escort GT or LX-E (with 1.8 dohc)
-91-96 Mercury Tracer LTS (with 1.8 dohc)
-97-Present Ford Escort & ZX2 (ALL MODELS, either 2.0 SPI or Zetec...all have a G-series gear box)
Cars with a different final drive:
-Ford Escape & Mazda Tribute (have like a 4.5x final drive...b/c they are trucks and use large diameter tires). dunno why the hell you'd want such a huge final drive.
SPLINE COUNTS:
28 splines are on:
MX-3 GS
Probe GT
MX-6 LS
626 ES (93-02)
MSP
26 splines are on:
basically all other cars listed above including the ZX2. So IOW If you plan to NOT get the LSD from the MSP, but want to use 4.11 final drive you need to get a differential from a MX-6 LS or 626 ES and use whatever 4.11 gearset you can get your hands on.
MORE INFO:
As mentioned above, the Escort ZX2 SR gears are apparently the best you can get in terms of durability and design. I am not sure if the 2.0 SPI also have these "updated" gears. Newer 626's might as well. I'm not sure what year these "revised" gears came into effect. I read 1998 on Probetalk but I honestly dont' know (and don't care to research)
AND SOME MORE INFO:
FYI I plan to remove the trans and fix a problem I have with the damn clutch fork this summer sometime. I PLAN TO WRITE A HOW-TO WITH PICTURES on how to disassemble a G-series transmission. There are a few tricks you should know but it is surprisingly easy if you follow the guidelines I will outline in the article. The factory shop manual's instructions are OK but there are a few problems I came into using them as tehir pictures sucked & the steps were vague as hell.
My how-to should also apply to basically any Mazda transmission including the F-series found in the base model MX3 along w/every other 323, protege and escort/tracer in existence. The design & structure of both the F-series and G-series are damn near identical so anyone could benefit from the article.
ASK QUESTIONS:
anything I'm missing? ask a question that hasn't been addressed and i'll try to answer it. I don't consider myself an expert w/transmissions. I don't know jack s--- about them to be honest, but I do know how to swap stuff out and undo bolts and such.............plus having 10000 spare transmissions to have fun with in my basement is a plus.
BTW: don't be surprised if I don't answer ur question if it has already been addressed above. I honestly hate when I have ppl ask me questions b/c they are simply too lazy to read my articles. I spent my time to write them so have some courtesy and at least read them before asking questions,
THANNKS 
faq ?
I swear, I can roll at 30 mph, hit the gas and break the tires loose with ease. But its only one tire... OUCH.