Pro Keys is a hodge podge of good ideas, waiting to coalesce. The app gives you two instrument areas, which can be set to play in opposing directions - allowing you to play with a friend. Theres a decent selection of sounds, and drum kits to boot - which play off drum pads. The interface is fairly straightforward with individual buttons to do everything - what you see is what you get - and you can customize by hiding interface elements you might not need, such as pitch bend - nice.
Theres the ability to record with overdub, but its pretty rudimentary. There are effects ... or rather, there is effect, as there is only a delay effect, and while you can set the delay tempo, better have your own metronome to play with.
The pitch bend is welcome, but any "pedal" emulation is absent. In the absence of a reverb effect, this makes the functionality somewhat limited if you were hoping to use it for "piano" purposes.
So in all, theres a lot on offer, and it all hangs together on the interface quite nicely and at a reasonable price - but the individual elements need some strengthening to compete with app store heavy-hitters like Pianist Pro, which basically eats Pro Keys lunch, except for the absence of opposing keyboards.
Post-script: For a peek at what these devs are capable of, go check out Beep Streets Sunrizer synth - simply the best soft synth in the app store - out punching Korgs behemoth iMS-20 by finding the sweet spot where power and usability align.