Tell me, I know they say the FS tensioner is not recommended for the Uly, but even FS themselves couldn't tell why.
Do you reckon it is worth it?
Wally, at GREAT risk of opening a can of worms on the FS tensioner topic, here's my perspective:
The price of the tensioner is about the same as the price of a belt (around here anyway), so if it saves me a single prematurely broken belt then it's worth it (to me). I had the same discussion with the guy at FS about mounting it on the Uly and the response I got was effectively -We didn't design it for that bike, but it may work. My thoughts as to why that is are that FS is a small operation and us Uly folks are probably a pretty small slice of the increasingly small Buell aftermarket pie, so it's probably not worth their time or money to procure a Uly just to see if it works.
The geometry on the Uly is effectively the same as the other XB models with a little more swingarm travel so installation is mostly the same. Mounting the tensioner on the Uly required removal of the rear brake lever, which you don't need to do on the other XBs and was not part of the instructions. That's the only difference i noted. Alignment with the paper-thin shims is going to be the same tedious task. Bear in mind that I have the Jardine exhaust which is shorter than stock so clearance was not an issue for me. It shouldn't be a problem for you either, you just have to pay attention to it during installation.
The way I see it, since belt tension is a function of swingarm position, with the Uly's increased swingarm travel it has increased variability in that department. It makes sense to me to have a tensioner that allows for more flexibility, which the FST does. So I got one. Now, I haven's sat down and cranked out the calcs to determine just how much tension variability there is, but the concept holds water for me so I went with it.
The ONLY concern I had getting one was the pics floating around of a couple units that had failed. The failures seem to be due to a poorly positioned dowel pin. So, I sent one of those pics to FS and their response was that the failure rate is less than 1%, the unit appeared to have been modified placing undue stress on the dowel pin, and they will replace any unit if it fails. While the thought of a failed tensioner on the trail is an unpleasant one, realistically a < 1% failure rate is probably as good or better than any other part on our Ulys (definitely better than the belts).
Now that I've opened the can way up for all the guys that have ridden a million miles on the stock tensioner, I hope I've answered your questions (albeit, in a a rather long-winded way).