Sounds to me that you're looking for a cheap fix which, at best, will end up being more expensive than you think. FWIW, I think I have heard of this device, but I'm sure it's no little $29.95 gadget. By the time you've bought it--and paid a plumber to install it--you will have paid at least 50% of what it would have cost you to do the job right; and then--who fixes it if it breaks down?
Do yourself a favor, at least get a few estimates for a proper repair (i.e. breaking up the concrete and replacing the 2" pipe with the proper size). The plumbing contractor may even be able to quote you a price based on *someone else* breaking up the concrete and patching it afterwards. You might know somebody who'd be willing to do this part of it for you for the price of a home-cooked meal (plus jackhammer rental, which is about $50). You might also consider a professional handyman, who could do the work for less than a plumbing contractor.
The benefit of this will be more than the *chopper* device could give you, even if it's installed properly and works perfectly.