I use the less expensive one. It requires a stop bar to be mounted on the table you are stretching on. The more expensive one is their original and is one inclusive unit with the stop bar and stretcher all in one so you can use it on any table. You shouldn't have to stretch them very often so you could easily mount the stop bar on a table just when you need to stretch and then take it off to use the table for other purposes. I would save the $$$ and go for the cheaper one.
Just as an aside, it took me a few busted panels to learn how to get them stretched correctly. The instructions weren't great but in speaking to them after they realized that. I'm not sure if they ammended the directions but you can use a little dish soap between the frame and tensioning bars to get them to slide into place a bit easier.