I tried one a couple of years ago and couldn't get it to work due to the sloped back and small soundhole.
Whoa glad to hear!
Now that I think of it, I was thinking about the Washburn Rover. It's similar to the backpacker but has a sloped back and too small of a soundhole.
Does this mean it will work on a Martin backpacker guitar? You know, the sort of elongated triangle shaped mini with a 2/5" soundhole...
The magnetic X-Brace that's mounted internally measures 3x3x1.25". If you could somehow manage to wedge the X-Brace and your arm into the hole, it could possibly be done. The smallest soundhole we've managed to install one through is one on a baritone uke, but I'm not sure what the exact size was.
ok thanks - sounds like it won't quite work then, for the martin backpacker (hey, new product idea: a very small version, more limited capability, specifically for small sound hole guitars!)