I have never played Psionics in any of my 20+ years of playing D&D. It's really just a choice more than anything else and I guess the main "put off" for me was back in the days of AD&D where someone with a psionic rating of 1 (highest back then) could pretty much have a field day with everything that didn't have psionics or was of a lower psionic ability....
I guess I just don't use it because the range of spells within the game (for me) contains enough variety...
I guess I am kind of like those players who flatly refuse to use prestige classes because they see enough scope and flexibility within the core classes (players handbook).
Me on the other hand, I don't think there is anything wrong with using psionics within a campaign if you want to. After all its there as an option to be used.
On the other note with your question about tumblers? Wouldn't using a reach weapon cut their chances of tumbling out down a fair amount?