These were my first experience with Ben Wa balls, and they did not disappoint! They are pretty big - it took me some trying to get both in. The naturally vibrating cores weren't enough for me to feel anything while I was just doing Kegels, but once I masturbated with these babies in the extra vibrations were heavenly. Doing Kegels with these in gives you more resistance, and your muscles will strengthen up in no time.
Like a previous reviewer said, these do have ridges where the two halves of the ball come together, so they are probably not ideal for anal use. Other than that, I'd recommend these to anyone.