I got a set of the universal type inertia reel ones from ebay a few years ago. They looked kinda cheap, sorta like what you would find in an 80's ear Japanese import, but they seem OK and do the job. There were two issues with them though. One is that the mounting tabs for the receiver stalks are oriented to be mounted vertically, like on the side of a tranny tunnel. Mounting them on the floor, like where the TR6 has threaded holes for this, makes the receivers come up next to the seat 90 degrees off, so you have to twist them a bit to get the buckle in. If you twist them very hard in a vice you can get them to stay where you want for awhile though. Second issue is that they are slightly longer than I would like, meaning they do not retract into the reel completely and there is a fair amount of belt hanging out. I just tuck the upper part of it between the headrest and the seatback whenever I get out of the car, and that way the buckle hangs neatly down the front of the seatback, which makes it easy to get hold of for the next drive. Overall for the price I'm pretty satisfied, they were substantially cheaper than the offerings from the big three.
Scott