I've had mine for a year now. Overall it's been working well, though lately I've been having increased urgency and feelings of constantly having to or even when my bladder is empty. I've got an appointment Monday to see the urologist and the Interstim rep.
When is working, you shouldn't feel much of anything. I occasionally feel a little pulse from it, which feels like someone tapping on my perineum with the side of a pencil. It's not painful when I feel it, though it can be distracting. If I'm feeling it frequently, I can adjust the intensity, since you normally should have it just below the point where you can feel it.
Peeing with it is completely normal - it's job is to moderate nerve signals, not to force your bladder closed. They actually use the same exact device and installation point for urinary retention, because it helps to normalize the signals from the nerves.
To use it, I select one of right programs (which all behave slightly differently, so it's trial and error to see which ones work well for me), then increase the intensity until I just start to feel it and back it of slightly. Kind usually runs at 0.4 to 0.5 volts, but anything under about 2 volts will avoid shortening the battery life. Then I leave it alone and largely forget about it, often for weeks. If it stops working well, I change the program, but other than that I mostly just leave it alone.
Mine is the newer MRI-safe Medtronic unit. I've had two MRIs since I got it, and I've had no problems. I use the controller to put it into MRI mode, then take it back out after the MRI.
My results have been good overall. I got it in November 2920, and I was able to quit wearing diapers in most cases by December (though I've still worn them occasionally if I know I won't be able to get to a restroom relatively quickly). My urgency has lately picked up to the point that I've had to start wearing them again, though hopefully I'll be able to get it dialed back in soon and be mostly done with them again.
