For the record, abs are made in the kitchen but I would never advocate scrapping direct core work!!!
I do heaps of direct core work, including obliques (often neglected by people because they're not part of the six pack).
Direct core work is great for posture, spinal health, and I defy anyone to suggest that it doesn't help with lifting weights!
If you've got a bad back, I'd suggest clinical pilates is a much better bet than the ab circle pro though. You get rehab to make your back and spine stronger, which the ACP does not.
imho
ps ab wheel rollouts are the shiizzz...strong core is my thang