Bikemonger says...  A nice bit of kit, just no brand name. You can get cheaper ones, but we have found these cheaper ones not to be that reliable, and we don't want to sell anything that will let you down. You will like this tensioner.

Spring loaded chain tensioner
Takes up chain slack when running SS on vertical dropout frames
Bolt fixes to rear mech hanger
Adjustable chainline
Drilled to save weight