It works, and it's not quackery. :-)
I've used the very similar Dent Wizard here locally and was THRILLED with the results. If the dent you have is just an indentation that's not too big, and no paint work needed, paintless dent removal from them will have results that will surprise the hell out of you.
The have these tools--long rods with handles, and a J's end on the rod with various sizes of smooth sorta like butter knife ends on them--that they get behing the door panel with. Using an artful hand, smooth out the dent from behind, and at least in the case of the 3 little marble sized indentations that were bugging the crap out of me on my door, they made them completely disappear for about $90 a piece.
I was very impressed and wished I'd taken a trip there sooner.
Best Regards,
-- Todd H.
2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA