Had the basic mini version before this, and upgraded to the plus as the only thing that really bothered me in the mini that the is only 2 octaves.
Build quality:- had the first one returned as the drum pads were really not responsive (I had the same problem with the regular mini, also had to return one of that one) As I read on the internet it is a common problem with AKAI minis, that the build consistency of the drum pads are not so great, so are better, some are worse. The replacement that I got is also not the best in terms of responsiveness, but I can live with it.
It has ton of features, and easy to handle. Got a sustain pedal as well, and it works great with it. The keys have a good feel for them. The chord and scale functions are really handy if you lack enough music theory, or not yet familiar which note is where. It gives you the ability to enjoy playing music earlier, so you remain more enthusiast, and on the long run it help you with learning the scales. So in this regard these are really good features.
Has a joystick, and two wheels, that can be programmed for different features.
All in all it is a really enjoyable midi keyboard.