I installed it on the front as they recommend, and I am using the narrower 100mm wide fork.
Compared with the original Endomorph tire, the Larry definitely has a "lighter" feel to it. On twisty trails, it tracks easier and requires less effort to make corrections. On deeper snow, it grips as well as the Endo. Even on ice, I could make turns with confidence.
If the Larry has one significant difference from the Endo, it has to be the importance of matching tire pressure to the conditions. Matching the correct Psi to the conditions was certainly important for the Endo, but I always felt that, as long as you were in a range, say 8-12 psi, I could generally ride over a variety of surface conditions.
Not so the Larry. It needs you to pay attention and dial the tire pressure in a little more accurately. Given the varied conditions I rode in this weekend, I tweaked the psi a few times. For example, 8 psi on soft oatmealy snow was just right but on the packed stuff, 10 felt better. The ranges are just narrower.
So, if you're on the fence about whether the Larry is worth the extra money or not, I say go for it. It really does provide a more "lively" ride, something the Pugsley could always use more of.