I think I'll go with a magnetic solution since it really will be quickest on-off both for fueling and for parking.
If you keep your motorcycle tank bag in the garage and you also use your garage as a shop or for various projects occasionally involving files and or hacksaws, then you'll need to fastidiously check the magnets for metal particle pick up. If not, sooner rather than later you will scratch up your bike. Yes lots of magnetic tank bags in use, and lots of scratched tanks as well. Be careful and find a system either to ensure clean magnets or frequent checking.
When metal particles do stick to the magnets, I've found that a thorough air gun blast is about the easiest way to get rid of them. Trying to pick them off or using tape is tedious and usually incomplete. That's 50 percent of why I went with the bags connection quick lock ring, the other 50 percent was to get the bag easily electrified for cell phone, etc. charging using the electrified ring.