I've got an A2090A somewhere or other and had been playing with it in an A2k and A3k some years ago.
It's an ST506 (MFM) controller and SCSI host adapter in one (XT is something completely different, like in the A590). It has no problems running with an '030 but has no way of coping with 32 bit fast RAM.
I've successfully tested it on my A3k with
Autoboot off - NoFastMem - BindDrivers - NoFastMem
Haven't tested it with larger drives (>200 MB) though or with something like a CDROM.
It predates the RDB standard and is completely incompatible to it. The partitioning software is pretty nightmarish, so I wouldn't even consider it for an otherwise unexpanded A2k... :-D
