What it is
The actual electro-pneumatic trigger system is pretty cool. You have to change the bottom line to one with a hole in both sides (supplied in the kit). The air comes into the bottom line and is split there, with one line going to the trigger system and the rest going to the valve system. The air that goes to the trigger system system first goes to a Palmer regulator mounted on the right side of the bottom line and from there through a tiny little hose to a banjo type bolt that replaces the front bottom line screw. From there the line goes up into the grip frame to another little tiny hose that goes probably a quarter of an inch to the intake of the trigger valve. The trigger valve is electronically controlled by a circuit board with two pots; one for valve dwell time and the other for firing rate. There are 3 dip switches that control the firing modes. The electronics are powered by either two 6-volt batteries or a 9-volt adapter. From the trigger valve there is yet another tiny hose that goes up to the pneumatic hammer device which slams forward to hit a valve. The valve contains a lighter than stock spring that rides a smaller than stock spacer/guide. The hammer forces the stock valve pin open for a period of time determined by the dwell time setting.

Owning an older Model 98, I had to drill out a section of the metal grip frame under the outer (plastic) grip on the left side in order to allow for changing the settings on the three dip switches for the fire mode and also to change settings on the two pots that control rate of fire and dwell time. People who do the conversion on any of the newer Model 98 Customs won't have to drill, though. The newer guns have pre-cut panels in the metal that just pop out with the tap of a hammer.
 
 

Disadvantages
One drawback I can see in this system is that it is not Co2 friendly. The tiny hoses are like fuel lines (the same as those used on the WGP Autococker pneumatics). They press on to little nipples and if the air/co2 were not regulated down to low pressure they would just blow right off. There is also a leaking problem when using Co2. As long as you don't shoot it fast for more than a few shots (say 50-100 rounds) without giving it a break for a few minutes it's ok. Otherwise the gas lines from the trigger valve to the pneumatic hammer contract at a different rate than the little nipples they attach to because of the co2 cooling as it moves through them and - three guesses - it leaks for a few minutes until it has time to recover.
Also, It would be wise to route the external air line that goes from the Palmer regulator to the pneumatic hammer controller in the grip frame in a way that doesn't lend it's self to getting hung up on branches and stuff.

As a side note, I stripped the threads in the valve body the second time I had the gun apart and had to call Tippmann to get another one. They were very good about helping out (as usual), but still, if the piece was made out of something other than light aluminum ( about the consistency of american cheese), it would be much easier to deal with maintenance on the gun. I mean, really.. common sense says that you should always make the actual parts out of something more substantial than the bolts and screws holding things together.

Advantanges
The advantages of the kit are the faster firing rate and unless my ears decieve me, a slightly quieter gun. When I say a faster firing rate, I not only mean the obvious addition of full auto, but that even in semi auto mode, the trigger action is incredible. Since the trigger is just an electrical connection, it's very, very light. You can fire as fast as your fingers and your feed system will allow you to go. Really nice. - Oh yeah... since the thing runs on compressed air, the velocity is really consistent. I
usually don't see more than 5 fps variation when chronoing - very often less than that. Another thing that is noticeable with the kit installed is that there seems to be less "recoil" when firing. I guess this is because there's less mass in the pneumatic hammer than there was in the original one.

Opinion
The gun works flawlessly in the field as long as you don't use co2. All in all, I really like the gun. I only wish you could use co2 instead of air. If they ever change the low pressure air line setup, you could do that. Maybe someone will come up with a modification for it.