gotya, I thought it was thin but i see now.. As to the tensioner...yeah the one i got wasn't anything but the kit tensioner with a small bearing.
It was way more expensive than it was worth but then again it's a toy lol. I do like the one you showed I had a mountain bike for a while that I took to one speed with a coaster rear wheel. If I ever do it again, I'll change the crank and the rear wheel or go with a tensioner like the one in the picture... the coaster wheel has the advantage of a brake so you get to lose one of the brake handles to make room for the clutch handle.
Before I do another one, I'm going to look around for one with spring suspension. The bike I have now is light weight steel framed and it just shakes my teeth.