Spinal nerve simulator?

Does anyone here have experience with spinal nerve simulators? I have arthritis in my low back, and my surgeon/pain management doc thinks it could help me a lot.

I don't know what kind of arthritis I have (stupid rheumatologists with their stupid 6 month waiting period) because I was just diagnosed 2 months ago (FINALLY, after almost a year of PT and steroid injections) and the current regimen of Mobic/tylenol 3 hasn't been fantastic. The pain doc is 90% sure I have ankylosing spondylitis, which freaks me out, but I won't know for sure for a while.

Anyway, on to the SNS. It sounds magical. I won't be able to do a trial until February, but I have to decide before the end of January which one I want... It's between Medtronic (fully MRI compatible, automatically adjusting stimulation) and St. Jude's (almost has the automatically adjusting stimulation, better levels of therapy, ability to update the firmware). The St Jude's sounds great, but I'm nervous about not being able to get an MRI. Any personal experiences out there?