I find it unweildly and too diffuse, but I've learned that aside from wands, I don't really prefer external vibrators with a "handle" - I feel it's like writing with mittens on, but some people like it.
Vrooms depend on how you're rating. It might be rated "5" if you're explicitly not counting wands, but it is only the tiniest bit stronger than the MiMi, so I would not expect it to be SUPER powerful.
Uma and MiMi are both pretty powerful and a high end for for vibrators that don't use AC power, so they're certainly not weak - but Uma is not really in a category above and much below the power of a plug-in wand.
Also, the e-sensual bullet is stronger than both of them, though it somewhat buzzier, but not as buzzy as the Pocket Fairy or a cheap bullet.