I've installed the Pro tank ring on both Beemers.
I think they're great. SW Motech offers a wide variety of sizes of tank bags, and all of them fit the same tank ring. We're both running the smallest Micro tank bag, but you can interchange it for any size SW Motech Pro tank bag and the new magnetic guide makes it a snap (literally) to put on and pull off. All without the bag touching the bike's tank and paint.
Only two drawbacks I can think of are:
1) most of the tank bags in the Pro range are not waterproof. The only model that is waterproof-rated is the Pro Yukon, but it's fairly large (6L compared to our 3L Micros). That said, I've ridden in light rain with the Micro, and while the outside material may get waterlogged, it would take a pretty big downpour for it to soak through and get the inside wet. It may not be 100% waterproof, but it's water-resistant enough.
The Pro tank bags do come with a little elasticized shower cap that you can pull over them when it starts raining, but I'm used to 100% waterproof bags, so this seems like a bit of an extra hassle. Another solution is to keep your water-susceptible items inside a ziplock or small dry sack inside the tank bag and just let the outside material get waterlogged and not worry about shower caps.
2) SW Motech warns riders not to use the Pro tank ring and bags if you're riding off-road in very dusty or sandy conditions. The locking mechanism may get gummed up with the sand/dust and you may not be able to get the tank bag off. Obviously, cleaning it with a good spray of water (all over your non-waterproof bag?) helps loosen the mechanism, but if you're on a trip and need gas and don't have a pressure washer...
However, I think this gumming up problem is not unique to the Pro tank ring/bags. I feel like any of the quick release tank bags will have the same issue, regardless of model or brand. And if you're just doing a lot of gravel roads and not riding *right* behind someone who likes to roost up a cloud of dust and sand behind them, then it shouldn't be a big problem.
Or just take the tank bag off if you're planning to go dune-bashing.