I don’t have any experience with Mega/Mattel stuff so far, so can’t really compare those. From what I hear, the quality of pieces is okay, but not on the same level as Lego and gobricks (the manufacturer that provides the bricks for both Lumibricks and Pantasy, among others).

If you actually want to give them a shot, just make sure you get relatively recent-ish sets (released within the last 2 years or so), as especially Lumibricks has very rapidly been refining the quality of their set designs, instructions etc, and gobricks pieces from before that time also tend to have quite strong clutch power which they’ve softened up by now. It’s really cool to see how quickly things are improving at the high end currently