I'm also looking at <$150 controllers, but I've been checking out the AKAI MPK mini. Doesn't look like there's too much difference in quality but I've heard that AKAI drum pads are always good.

You absolutely can learn piano on 25 keys, dont limit yourself. Once you know your way around the 13 keys in an octave, it's just repeated up and down the keys.

Would love to hear from someone who had experience with some of these controllers