Bikemonger says....  Damned tough tensioner that holds the chain in a fixed position (its not sprung like a Surly).

Great for jump bikes etc.

The roller makes a slight noise when the chain rolls over it - but this is easily fixed by stretching a cross section of innertube over the roller. 

Unreal value for money.

Gusset says.... Fixed position chain tensioner for rigid frame and hardtail bikes.

Designed to fit with regular QR system Skewer set-up or 10mm axle without supplied QR nut.
Includes replacement end nut for regular QR. 
Super light alloy body. 
Simple pivot & lock tensioning.
Wide chain line position PU chain roller.
Sealed bearing.