IMO the tensioner is more trouble than it's worth and a safety hazzard. Specially if your bike has regular droputs so you can move the wheel back-and forth. Between that and half-links there's no reason to get involved with engine shims either.
Exactly!
It never made sense to me to put a tensioner on the main drive chain.
Sure, it's easier, put why put an extra moving part on the chain that is always in motion?
I size my drive chain to fit with the hub bolt about 1/4 to 1/3rd of the way back in the frame slot and adjust the pedal chain accordingly.
On a brand new bike, chances are your pedal chain will be too short like mine, so I added a link pair.
I just used a link from the extra chain from the drive chain and the kit included extra master link.
At first I just put the tensioner on the pedal side and it works great for that first 20 mile or so chain break-in period. You could of course just leave it on and it will never wear out, but it didn't make sense I couldn't get the pedal chain to match so I did some research.
Low and behold I found the Half Link.
What a wonderful little $1.99 fix!
This is the pedal chain with the extra link pair that requires a tensioner.
This is it on the bike using the Half Link.
Here we are with the drive chain snug, and about 1/2" slack in the pedal chain.
As the drive chain stretches more I can just move the wheel back.
Tensioner? Pffff... We don't need no stinking tensioners ;-}