I agree with rkauer. I've tried 3 68000 accelerators: a hack from aminet, ICD's AdSpeed, and Supra's Turbo28Mhz.
The hack from Aminet seems equivalent to your accelerator. There were some chips to massage a few of the 68000's control lines and a switch to flip the clock. There was no buffering. The clock was doubled but the performance was NOT. It made my A500 barely usable.
ICD's AdSpeed was a little better. It had some buffering on the accelerator. It worked with fast ram, gave a noticable improvement, and was fairly reliable by itself. It seemed to work with A570 for about a week. I killed 2 A570s testing this configuration. I don't remember getting it to work with any other SCSI expansion either (GVP or Supra).
Supra's Turbo28 was much faster and had twice the buffering as ICD. It seemed more reliable, too, though still incompatible with A570 which is picky about timing. It is currently installed in an A2000 and running well with A2091 w/2Megs of fast and V7.0 roms, OS3.1. This machine does take a long time to boot though, about 1 minute!
A 32-bit accelerator is the way to go if you need more than the allowed 8 megs of fast ram.
