Both have their ups/downs IMO.

Pros to the Passon unit is he's got a great reputation for being one of the good guys in the hobby and he stands behind his products. Plus like mentioned already, it's a stock replacement trans, so you can reuse everything else. Cons to his piece are the o/d gear is only a .80. Now I think he did that to keep the gear spreads reasonable for performance driving, but it does hurt his o/d's usefulness on the highway. However, if you've only got a 3.54 rear, you probably don't need as much of an overdrive ratio as say someone with a 4.10.

Pros to the keisler is their available .64 o/d. That really knocks down the RPMs on the highway, and the extra gear of a 5sp makes it so you don't have to worry about far gear spreads, because the race will be over by the time you are at the end of 4th anyway. Also their trans will have a more modern shift feel to it. Cons is you have to change a lot of components to make their trans work. That trans doesn't shift well if you rev your engine much over 6k rpm from what I've heard. If you do a search you'll see some members who've had problems with this trans, though I think most of them have been since resolved by keisler.