Review on DMR Chain Tensioner Stainless Steel by Andrew Agarwal

Well made and durable. No springs or anything that could break later. It's a little pricey, but it's also worth buying others that break or don't work as they should, only to end up buying this one. I just bought a second one for another MTB. Only works with 9-speed chain. Single speed chains are too thick to fit in the idler pulley. The narrow, wide chainring in combination with the long stainless steel sprocket eliminates any chain slack. Locktite can also help if aggressive pedaling causes your bike to wobble a bit. Driven 200 km without problems.