Magnetic is no problem at all, and if you're savvy and patient, you can pick up a decent one brand new for $30 (CANADIAN in my case!).
They have a strap you're supposed to clip around the steering head, but I've never done it, and never had any issues at all. Only time I've had one slide a bit on me is when I DROPPED my Concours, and while picking it up I moved the bag. But it's magnetic, move it back and away I go...