Here is the reason why i designed my own chain tensioner; only because no other professionally designed product existed that could be added onto the SickBikeParts shift kit without modifing the shift kit in any way.
This design is a simple bolt on device to the existing shift kit clamps.
Very effective in operation and so far the tensioner has 6,000 kilometers (3750 miles) of operation without failure.
I still use the original threaded rod tensioner to set initial chain tension (and to assist the clamps in preventing the engine walking down the seat tube) and from thereafter the chain tensioner takes up any chain stretch for a good 1,000 kilometers (600 miles with regular lubrication) before i need to check the chain for mechanical wear and stretch.
Chain Tensioner - SickBikeParts (SBP) Jackshaft Shifter (Shift) Kit - MotoredBikes.com: Motorized Bicycle Forum