I like to go on long rides, 100-200 miles per day and I hate having to stop and adjust my chain tension. For that reason I love spring-loaded tensioners. However, my setup uses a centrifugal clutch. For bikes that have a manual clutch (and can thus engine-brake) when the load on the chain gets reversed as during engine-braking, the bottom side of the chain will be under tension and the top side will go slack. because there's no tensioner to take up slack on the top, you can risk throwing a chain when engine braking.
Here's a pic of one I just made for use on a Staton gearbox driving a freewheel crank: