On the druid both the guide and the idler touch the chain (although I saw a forum post somewhere where someone claimed they haven't had a guide on their druid for a year including bike park laps and haven't dropped a chain).
I can't 100% say if it was noticeable in my short test ride. Felt like I could tell, but I wasn't back-to-back comparing bikes.
Could absolutely feel it just turning the pedals forwards and backwards by hand though, and that was on a clean brand new drivetrain. If you can feel it, it definitely costs you a few watts of power output. Somebody at pinkbike did a double power-meter test between a Dreadnaught (idler and chain guide) and a normal-pivot and found a roughly 2% power loss between pedals and cassette.
Is 2% enough to care? No idea. On the road, people will buy ceramic bearings and oversized derailleur pulleys to save a fraction of that, but unless you're racing I'm not sure it matters compared to how much you like riding the bike. On an hour-long climb, you'd be like a minute and a half slower?
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