Me from the future here; I ended up settling for Magnet
It has nice logical shortcuts to snap windows to quarters, halves and thirds of the screen and supports dragging to the edges of the screen, like in Windows. Easily worth the 1.09€ for me.
Ended up switching to Divvy. It allows me to place windows anywhere on a customizable grid (kind of like a less aggressive tiling window manager). And I can define custom shortcuts. So I took Magnet’s shortcuts and added a whole bunch of other ones, like centering, top left sixth, bottom quarter, etc.
It also allows to set a custom window separation, which I think looks pretty good.