We actually made our own version of the AndyMark style, without the rubber band fingers, but still using the zip ties, and it worked quite well.
There is another page of chain tensioners at McM-C, with a more expensive and sophisticated variation of the AndyMark one:
http://www.mcmaster.com/#chain-tensioners/=74adn5
Go to page 1022, or part number 5973K2