Okay, I found one of these and have been playing with it for a bit and here's my take on it.
First, THIS THING IS A BEAST!!!!!
I mean really, it's HUGE!
Take the lowly A500 and stick this on top of it, and you've suddenly doubled the depth. With the BB attached, the A500 is a whopping 23 inches deep instead of the typical 12 inches.
The height is also monstrous. In the corner computer desk I use for the "Amiga Corner", with a 15" LCD monitor, I have about 1/4" to spare! Much taller than an A2000.
About the only advantage to this thing is the zorro slots with the ability to add a bridgeboard. However, even that's not a big advantage due to the GVP 286 board for their sidecar peripheral or the ATOnce card that fits where the processor is in the 500.
All in all, I can confirm why this thing didn't sell real well. Way too bulky.
Of course, that's just my 2 cents.
Curtis