I have the Bags Connection, City Model, tank bag for my 2013 BMW R1200RT and have had it now for over a thousand miles of use. As we know, the RT is fitted with a rail system on the tank which will hold the BMW tank bag. The two closest dealers (275 miles and 330 miles) did not have the BMW bag in stock and I hesitated ordering it online since it looked too big for short weekender trips. For the price, I didn't want to end up with a bag that I wouldn't use on a regular basis. So I opted for the Bags Connection tank bag. The base fits right over the gas cap base and mates to a similar base on the tank bag.
The connection is really solid and it's not loose once it clicks into place. My fit is near perfect as there is no extra space between the bag and the downward curvature of the tank. I looks like it belongs there. As I mentioned the bag is secured to the base by a pin which is tensioned by a spring so that it won't open on its own. The bag just clicks into place without having to pull the pin outward. To remove the bag you do have to pull the strap that's conveniently connected to the pin and the bag just lifts off the tank base. Did I mention that it's really a secure mating of the base plates!
Installation is very simple. The base plate on the tank only requires that you pull four screws from the tank's ring that is around the gas cap lid and place the base plate over the tank's ring and secure it with the longer screws provided with the base. The base on the bag is a little more complicated since you have to decide where you want to place the mating base plate. Location of this base plate determines how far forward or back the bag will sit on your tank. I placed the bag over the tank to help me determine where to locate the mating base plate. If you get it wrong or don't like how it sits on your tank all you have to do is move the mating base plate, but that will leave a set of four holes through the bottom of your bag so it's best to get it right the first time.
The bag itself is a medium sized bag that's perfect for my quick to grab stuff like my cell phone (on the front separate pocket with the port to run your ear bud cord through), garage door opener, flash light, ear plugs, sun screen, lib balm, towels for wiping down bike, and my cap. The two side pockets are for my receipts and any medicines/vitamins. It sure beats having to reach into your saddle bags or the handy right hand pocket on the fairing that's nice, but too deep to keep any smaller items or bigger stuff like a cap.
The beauty of the Bags Connection is that you can buy different sized bags, including a very small tank bag for short rides that will hold your phone, change, and other smaller items. From there you can go up to the larger bags that are made for those long cross country rides.