Oh, the basic concept for this tool is really nice! :D
I use Affinity Designer and it does have a 'pixel helper', but it's way different than this!
Besides helping with pixel art, I can totally see this as a helper tool when working with font design (specially with pixel hinting).
Great job there! :)
P.s.: out of curiosity, are you developing it in Haxe? :D Nice job there! It's really motivating to see projects made with it, since I really want to get deving in it.