Props to the developer: it's simple on the outside, and solid on the inside. I did look at the code, it's very well organized and shouldn't cause any issue down the road.
Makes the dev work dead easy, and the user experience is really good too.
Being able to localize or customize the error messages and field labels would be a plus, though. But that's the only options i would add, as this is one quality of this plugin: works out of the box.