I bought the Evo Clutch upgrade for my left Gladiator NXT base, as the last GNX Unit I purchased was not nearly at the same level of quality as the other three. The internal detente had broken off and therefore I had no centering on the Y axis.
The new base itself was not subject to these problems. Installation wasn't exactly easy, but it was fairly straight forward.
Tuning in the clutch can take time and be a bit of a pain. I didn't find I liked the handling any better than my other NXTs, and it produced a somewhat incosistent range. There's also the strange feeling of cords being squashed when fully deflecting the stick to the left. It has also locked up on me several times in flight where the stick would not deflect right from centre. These episoides have been few and far between though.
Overall, it was convenient if somewhat expensive method of fixing the inferior base I had received earlier. Having to open the base to access the clutch adjustment is less than ideal, and the kit itself didn't include the allen key, so I had to make do myself with one from home, which mad the process a bit of a nightmare.
All in all it does what it says on the tin, if you prefer the dry clutch feeling, then go for it. If you've got working NXTs presently, then I would say the upgrade is superflous.