Pipe clamps aren’t the optimal clamp to use for glue-ups, but they are cheap. You can usually buy three or more pipe clamps for the price of one parallel jaw clamp. Plus, they’re very versatile — you’re only limited by the length of threaded black pipe you have on hand. Some of their downsides are the jaws don’t always stay parallel and the workpiece can buckle if you’re not careful to support both faces.
Pony’s double pipe design attempts to remedy these shortcomings by using two pipes instead of one. The clamps straddle the glued panel, keeping it flat. The pipes are spaced wide enough apart to accommodate stock up to 3″ thick.
The hardware for one double pipe clamp retails for $36, pretty much eliminating the advantage of being more inexpensive than a good parallel jaw clamp. So whether you’re better off with one of these double pipe clamps or a parallel jaw clamp will probably depend on your particular circumstances.