I had a Manta on my old Red Strom for almost 2 years with no issues. It's a great little bag. I've read that if you have a metallic paint that you don't want to keep a magnetic bag on all the time. You should definitely get a good coat of wax on before using the bag just for some extra protection. I also bought a bra and never used it cause the lower magnet covered the tank just fine, and I was worried that leaving a bra on all the time would damage the paint.
Red 2006 V-Strom 650: "the most shockingly competent machine in the world today"
Alpenkönig (a.k.a. King of the Alps): 2005, 2006
1989 Sportster Bobber Hardtail
1990 Electra Glide with Cop Bags