The FreHD emulates a real TRS80 hard drive, so you don't need to use custom drivers. It uses a FAT on the SD-card, and the image of the hard drive is compatible with the TRS80 emulators, so you can prepare/fill your hard drive image on your Mac/PC and use it directly on the real TRS80. You can also have multiple hard drive images on the same card, backup of your hard drive is easy, etc... The price is that you need more hardware (GAL/PIC), but you have more flexibility...
On the price side, a GAL and a PIC are cheap, but you need a PCB, etc... The design is open sourced, so enthusiasts can rebuild it. (At least one guy recreated it on a breadboard...)