Designed primarily for running on singlespeed bikes with vertical drop-outs (not fixed or those with coaster brakes, though), my Singleator has been in use for many hundreds of miles on my Airnimal Chameleon folder that I converted to hub gears. And it’s worked faultlessly.
While the Chameleon frame allows for some minimal chain tension adjustment in the form of semi-vertical drop-outs, the chain still needed to be kept under tension during the fold.
The Singleator will fit most derailleur hangers, with adjustments for both chain line and spring tension, making it very flexible. Two spring options are also included so you can have it pulling up or down as you wish. I liked the deep anti-jump plates either side of the cog to keep the chain firmly in place, the quality stainless steel pivot bush and the fact it accommodates both 1/8in and 3/32in chains. The Singleator seems a bit pricey for what it is, though weighed against an eccentric singlespeed hub (a more elegant solution for non-folding applications), it’s obviously a much cheaper option.