TDLR: Super addictive, charming puzzle game. Worth the money (even more worth if it's on sale).
Grindstone is NOT a Bejeweled or 3 matcher type game. It's about creating paths between creeps of the same colour, and creating huge combos to complete objectives on the maps.
I last played Grindstone a couple of years ago on Apple Arcade (20hrs+), and it's just as great as I remember. They've added a lot of new features (dailies, hats etc) since I last played.
Yes It is a port of the mobile game to PC, but it doesn't have ANY mobile game BS (ads, micro transactions, etc), and the controls work great with mouse.
Worth the $20, but should probably be cheaper ($10-$15 would be perfect). I got it on sale for $5, but I wouldn't have any regrets if I bought it at full price.
The only thing I don't like is how potentially easy it is to click the "Erase save" button in the settings menu, it seems like that option should only be available on the "Choose a Save" screen when the game launches.
The game speed (animations/scrolling) appears to be tied to the frame rate, so run it as high as possible (180fps in my case) for the smoothest experience.