I'll remember that every time i use it
Please do.
PS The best tank bags I have used? Certainly not the BMW offering, for exactly the same reasons as in the opening post. Not the ones that engage with a horseshoe ring thing, that leave the bag perched up like a ping pong ball on.... nor the magnetic ones, that attract metal (like your keys) with an attraction that is, well, let’s say, magnetic.
Which brings us neatly to the offerings from Touratech / Wunderlich, whose much simpler bags I have used for years. Easy to take off and put on or just ‘flapped up’ (forwards or backwards) and above all reasonably interchangeable between bikes, despite their apparently different tank shapes. I have the small ‘City’ bag that I’ve had for years, that has been on assorted bikes (Honda Blackbird, SP2, CBR 600 RR) and then GS / GSA up to the twin cam (I have never owned the twin cam or WC iterations of the bike) and on an HP4, my 1600 GT and HP2 Sport. Similarly, one of their larger bags, which I use on several bikes, too.
Rather than buy several bags, I just contacted the maker, obtaining from them the pads that hold the front of the bag on, the rear only being held on by velcro anyway. The spare front pads I just velcro into place on each bike. They have never come off in many miles of use in all weathers and temperatures.
The ‘City’ bag I have had for so long that I forget when I first bought it. So long in fact that eventually the zip failed. Rather than buy a new bag, I had a dress repair place sew a new zip in for a few pounds. Measure the zip, find one of exactly or near enough the correct length and with the right sort of teeth, which you can do on the internet or with a bit of patience in the haberdashery department of most large stores; job done.