I was never successful making a helmet mirror work for me. It was extremely hard for me to shift my focus from looking ahead, to the mirror. I wonder if it has to do with which eye is dominant. Trying to use a helmet mirror while wearing glasses might have compounded the problem.
I got a Mirrycle just like yours, and I'm guessing the shop will be able to make it work for you. Mine is on my "road" bike, which is basically a sporty looking hybrid with swept handlebar. Unfortunately, there's so much variety in bike components these days, that there is no longer a "standard" that allows any accessory to fit any bike. So it's always possible that attaching something will require a bit of finagling.