I have Mechy's SCSI card readers in both my 500 (via GVP sidecar) and 2000 (previously via GVP '040 board, now by '060 board). I think the trickiest thing for me was figuring out where to put it on the SCSI chain, and termination. Make sure the termination jumper is on if you have it as the last device.
Everything works once you get it set up properly, LUN's, hot-swapping cards (except for your boot card, obviously), great piece of hardware. Just keep playing with it, it'll work. You might also want to update your ROM's on the 2091 to a newer version.
