This was demonstrated on diynet..
The process is no more complicated than creating a dowel joint, (and in fact, the drill jig could be used to create dowel holes if desired.) The secret is that once the jig is clamped to the workpiece, and you drill a set of holes, there is a slide mechanism, that allows the jig to move exactly half the distance between the holes. Sounds complicated, but after watching a demonstration, it is a very simple process.
(shims are provided in the kit, if offset tenons are to be used.)
http://www.beadlock.com/ sells the jig and the necessary router bits to create just about any size, or length of loose tenons, that you would desire or you can buy the tenon stock premade. (The router bits to make the tenon stock cost more that then jig...)
I have NOT bought one of these, yet, and I would certainly appreciate any downside to the system, that I'm not seeing.......