I laser cut a few of these cutouts onto some cheap eight inch hardboard/masonite to test them out, including the new H-shaped one. They are pretty loose though since hardboard isn't a very precise material for laser cutting, the burning made the cuts wider than I wanted. With the loose holes the one with both corners and tabs is the most stable, with the H cutout being the least stable.
I've attached some pictures although I'm not sure they will show much. The one with corners and tabs has very little lateral and rotational play unlike the others, but all the holes are very loose vertically since the board is too thick for the switches to snap on and not tight enough for a good friction fit. The switches don't fall out but you can't pull keycaps off of them without them coming out.
I used jdcarpe's CAD files for all three cutout types, cut on an Epilog laser with 15% speed and 100% power.
Takeaways:
- Hardboard is decent for prototyping plates, really cheap, but too imprecise for actual keyboards.
- Without tight tolerances, the H shaped cutout doesn't hold the switches as well as the others.