Honestly the only """negative""" thing I can say on here is that the picture's a bit old -- they're all pink plastic instead of blue, now.
Other than that? Does exactly what it says on the tin! Lots of speeds (not functions -- *Actual Speeds!*) and surprisingly long battery life. I have a bad habit of leaving them in, but it's gone quite a while and a good many uses and I've yet to need to change the batteries!
While normally I'd go for a wheel or slider vibe, just personal preference, this has become my new favorite due to lasting power, actual *vibration* power, and ease of use, combined.
Now I just need to get the double-bullet version for my partner and I to use together ;)