Richard,
I have one (there are a few threads on this subject also) - is it worth it?
It depends on what else you've done. I would expect that they are only really useful if you've gone for new headers, more open can, and K&N filter. If you've made thouse mods, it does protect the engine from running lean, and does make a significant boost in performance.
Overall I would say that it is worth it - but it's personal. The good news is that, if you don't think so, you can take it off and sell it (someone was looking for one in the For Sale & wanted Section).
Cheers,
Dave.