I played it a couple of days and it's great. I agree about the selecting the different tiles, it's not the smoothest but it's very easy to understand how that works. The whole puzzle really explains itself well with the numbers turning green. I love how I'm building a set of heuristics (this space only fits a horizontal, if I need X points on a vertical, I need doubles...) in my mind to solve these puzzles step by step, just like with a sudoku, but very much it's own.

Maybe tapping on the left selects the left piece, right the right, and middle toggles? But that's just booked shedding. Great, polished puzzle!