Best way to mount metal boxes on EMT run through 2x4 framing
If you can drill straight through to run longer chunks (or if not able to, a bunch of shorter chunks, and couplers, and perhaps slightly oversized holes in some studs to facilitate getting them in) you can just run the conduit in a straight line at the elevation you want the boxes at, and run straight into the sides of the boxes, rather than using a bunch of elbows up into the boxes. This does involve working your way along to do the install, since you can't easily insert one in the middle of a run that way. But if you build it as you go, it works perfectly well, and is shorter, with fewer bends.
The &quot;crushed corner covers&quot; are exposed work covers, intended for use without drywall or trim plates. There are different covers intended for use with drywall or plaster, commonly known as mud rings and coming in various depths/extensions - and then used with normal trim plates for the devices to finish the opening around the devices in the drywall/plaster surface.