The problem with those side expansions is that the A500 isn't capable of generating a proper 5V at the slot. I had to connect a separate power supply to my slingslot to be able to run most zorro cards.
You need a minimum of 4.5V, and my A500 could only drive the slingshot to about 4.1V. The only card I could run without the external power supply was the A2090A SCSI card.
