We had a setup like this at our field too. There was one huge problem with it that made it more trouble to use than it was worth. The bracket that came with the glider was only about 6" or so wide. The problem with this is that whenever you turned the trainer/mule aircraft the glider would "fight" the turn, it would lift up off of the bracket in turns. We had to have the glider pilot make the same turns as the trainer pilot did to prevent this from happening. It took a lot of communication between the pilot and the glider pilot to make turns. It turned out to be more trouble than it was worth, and we gave it up after 3-4 days of trying. While I haven't had the chance to fly one yet, I have seen the same setup with brackets that were > 2' wide and they didn't seem to have any of those problems.

So in short, if you bracket is less than 24" apart then it's not really worth the hassle.

Ken