I may be a little late to the game, but I'd be ecstatic to be able to be a tester for something like this! Call it the StretchMaster (like the [words=http://www.mattersofsize.com/forum/showthread.php?83577-Length-master-official-order-thread-now-shipping-06-16-2014!!!]Length Master[/words])!
I would say comfort is probably the biggest concern I would have, then price. Also, how easily it could be seen through clothing. I work in a professional environment, and seeing a bulky stretcher under my clothes would be bad news. Seeing a bulge is a completely different story though haha