The main point the Fairy Mini has in its favor when compared to the Hitachi is its controls. Instead of a low/high switch, it has a wheel that lets you fine tune the speed as much as you like. The vibrations are extremely strong, and from my perspective, even stronger than the Hitachi.
The only downside I can find is that if I use it for too long, my vulva feels a bit tingly, but I have to have it on for a really long time for that to happen. Also, since I have a king size bed, I've found that if I scoot too far away from where it's plugged in, the cord won't go any farther. Also, it's pretty darn loud, especially when I have it pressed against something. However, it's incredibly easy to use and fantastically strong, so the good definitely outweighs the bad.