I like the idea , but there is a lot of drag and there is a constant ratcheting , so it always ticks away and there is extra wear . Add the weight , massive Q factor and having to modify the frame to fit one I'll say no thanks .
Another thing that at first I think wow that's just what I need but after a little thought I'll just stick with the one ratio drivetrain
Have you had a look at the schlumph cranks ?
"It also has a seat. I don’t use it, but you probably will for the first few years until you build up the muscle."