On the Korg site you can read this:
Slim, lightweight, USB bus powered, and compatible with all computer-based music software, the microKEY is a great way to create your production setup.
So I get one to play on my iPhone/iPad synthesizer apps and it seems what was written is true. It is compact, compatible and plays nice. The keyboard is also cheep but keep in mind that you will need Lightning to USB Camera Adapter by Apple so you can connect it with your iPhone or iPad. This adapter will cost you almost the price of the keyboard 🙂 (You will need that for any USB keyboard)
Now to the bad things, that were not written on Korg’s page. To bring the price low Korg have turned to cheap and average class matherials. The keyboard feels and looks more like a kids toy than a musical instrument. However the playability is not affected and you will be surprised by how nice and well it plays. I also like the Pitch-Bend joystick as it works really well.
So for that price Korg microKEY is the best compact MIDI keyboard you can find for your iPad/iPhone.