Today I got out for a proper ride on the Fuego with the new tube-free chainline (see here for details). It’s a keeper. There’s no problem contacting the chain with your leg, and you only get chain/wheel contact on really tight bends such as switchbacks or u turns. I imagine even that will lessen if you put smaller tyres on – the Marathon Racers are pretty beefy.
The chainline is now really quiet – just a little noise off the power idler on big gears as before and the occasional contact of the chain on the seat bracket still. I might try to put a bit of rubber on that just to quieten it down. The new Terracycle idler works beautifully with no discernible noise at all.
I don’t think it’s made any measurable difference to the bike’s efficiency, but it ‘feels’ faster knowing the chain isn’t getting dragged through 2 gunky tubes. Good enough for me! Next I might get some go faster stripes.