One difference I've noticed is that with Magnet, if you have a window 'maximized' by dragging it into the top of the screen or pressing the shortcut for it, when you start dragging it down from the top of the screen to unmaximize it, it instantly returns to its original size, whereas with Rectangle it stays maximized for some time after you start dragging it which is pretty annoying.
Another thing is the way Magnet moves and resizes windows seems to create less visual 'flashing' than Rectangle's method, for instance Rectangle will resize, then move, then resize again when maximizing a window, which can create a really pronounced 'flashing' effect. That's not to say Magnet has no 'flashing' ever, there's certain situations where it does and to my understanding it seems necessary due to the limited nature of moving and resizing windows on macOS (I guess you have to do one then the other and can't both move and resize simultaneously?), but to me Magnet's methods often look visually better.
Rectangle is great though, I've switched to it from Magnet and these are just some minor gripes.
Good to know! I'm surprised that Magnet has any improvement over Rectangle in these areas, since Rectangle isn't really adding any overhead to the Accessibility API commands, but I'll have to investigate.
Another thing is the way Magnet moves and resizes windows seems to create less visual 'flashing' than Rectangle's method, for instance Rectangle will resize, then move, then resize again when maximizing a window, which can create a really pronounced 'flashing' effect. That's not to say Magnet has no 'flashing' ever, there's certain situations where it does and to my understanding it seems necessary due to the limited nature of moving and resizing windows on macOS (I guess you have to do one then the other and can't both move and resize simultaneously?), but to me Magnet's methods often look visually better.
Rectangle is great though, I've switched to it from Magnet and these are just some minor gripes.