Remind me what drive/firmware you're using. This new "MK" firmware is basically the latest firmware for each drive (the ones that became non-UHD friendly because they patched that out of the firmware) that's been patched by MikeCH from MakeMKV to restore the functionality. In the case of some drives that restores UHD friendliness, as well, allowing us to use the latest firmware and retain UHD friendliness. In the case of the ASUS drive, the latest firmware fixes bugs so a bunch of us have switched to using it. You can, of course, cross flash other drives to that firmware if you wish depending on your drive.