I was testing about the theory of using cover can shows boot screen without a Mac EFI GPU. I wasn't quite there yet. However, What I found is that cover make the USB 3.0 card (KT4004) actually working BEFORE OS loading. The screen was totally black, because I intentionally do the test with the PC BIOS on my 7950. However what happened was. 1) I clone my primary SSD to the test HDD 2) install cover (all default setting) on that test HDD 3) select the test HDD as boot drive in system preference 4) restart 5) I hear the chime, but black screen only 6) after few more seconds, all my USB 3.0 card reader / HDD enclosure works. LED indication shows the SD cards and HDD should be mounted. Since I did the test with a HDD, it will cost minutes to load to desktop. And after the chime, the computer seems waiting for my input (HDD quiet). So, it's impossible that the computer already boot to desktop. Also, I actually gave it few minutes. And then press Enter (assume cover is there but I just can't see it). The computer then shows the loading screen as usual (macOS Sierra) and continue to boot to desktop. After that, I confirmed that was boot from my test HDD. Since I don't have external bootable drive on hand now. So, I didn't continue on investigating this matter. However, I think quite a few guys here will be interested in it. So, if you want USB 3.0 bootability, please try cover, and report back.