I love the idea of the hold-downs Doug - my mini versions are here, (no screw holes) but as I said in the text - I actually don’t like them!
I experimented with open sides but found the print time was actually shorter closing them in, and in the end the stackable feature was ignored (by me) because I tend to just chuck 'em in a drawer!
I like to just whack in a brad on the board and bend it to suit whatever I’m doing and no fussing with the pyramids, so mine ended up in my grandkid’s Lego. (don’t stand on 'em!)
Not trying to rain on your parade but have you found they are worth the effort of using them? I was pretty disappointed!
https://www.printables.com/model/208833-micro-painters-pyramids