Many bikes out there come with some big chain line issues, or a SRAM Red derailleur (sick burn!). Either way, you'll be dropping chains like crazy and this is a cheap and inconspicuous solution to that problem. I only gave it 4 stars because it's difficult to install.
Product is nice and simple. Installation was easy and very straightforward. Worked great on my AM Hard Tail but did not work so well for my Titus Motolite! running 1x9 on both When it worked it did its job..
There's not really much to say except that it works on the four bikes that I've tried it on. I now have one that resides permanently on my cross bike, my 1x10 Rip 9, and my two boys 1x9 mountain bikes. I've tried other similar devices that work well too, but none were this cheap.
Easy to install and adjust. Works ok. Chain can still come off and get past the watcher. That said, it dose help prevent most issues