I have a GS bag on my GSA. After 3-4 years it is faded. The main access zipper has crapped out. I plan to get the zipper replaced and use the bad some more. I want to get the newer EVO GS to replace this, but I went and bought a nice used BMW GS bag that has the old stretch band crappy mount but look pretty and now I'm invested on that for a while, but will probably use the Engage bag again once my local luggage repair/shoe repair guy puts in a new zipper.
The mount system works great, as intended, a bit stiff to get on and off when overstuffed as it always is at gas stops, etc.
I tried the electrical ring, but screwed it up when I though the relay wasn't working, and i don't think the little pins are worth much. I now have an SAE wire coming into the bag through a powerlet port and that works great for charging lots of stuff at the same time, like iPhone, iPad and even my Sena when it runs down which is never.