Re: benefits/ disadvantages of tensioner-less chain?
i never use tensioners. venice's shim method works great, and i have a stock pile of different toothed rear cogs for coaster brake hubs, as going up or down a tooth will take up a half inch of chain.
i find it smoother, cleaner looking, and less drag. not all bikes will work, sometimes the chain will drag on the frame's chainstays, but with some patience and experimentation, most can be made to fit.