This watch is an awesome tool for keeping in rhythm in a quick and easy way that's always on your wrist. The metronome itself is super easy to use and the vibration is more than enough to feel when playing guitar or drums. The tuner works fine but isn't perhaps as "fast" as other options (pedals etc). It comes in avery neat package and you get a few extras as a bonus.
The only real downside is that is doesn't have nearly as many features as a "regular" smartwatch. It's in that way sort of a one trick pony, although very nicely put together. I bought one for myself as a main watch and just recently but another one for my dad who isn't in to the "smart" products anyway.
I would strongly recommend the Soundbrenner if you're a musician, although perhaps not if you want a fully fledged smartwatch experience. I would also get the steel version in favor of the regular one, as it's more durable and sturdy feeling.
All in all a very clever idea and a nice experience.