Not overly familair with Formula, other than having ridden (and been very impressed by) some original The One's a few years ago. Well, that and have seen some older Formula's corrode and seized in the workshop and require replacing. So my experience so far suggests high performance, but relatively high maintenance (but probably not as high maintenance as Avid).
Anyway... Looking at some new brakes for my 29er right now, really tempted by some Formula's, especially the T1s. What's the real world difference between the T1 and T1s though? Just a cheaper master cylinder? Worth spending the extra on the T1 or just go with T1s? Or what about the R1 and R1s?