I finally took the opportunity to try out the Tailfin. It was actually a situation perfectly suited to the system's convenience, a local frame builder and his wife hosted a potluck so my wife and I considered it appropriate to ride over on our bike's that he'd built, i.e. not my BMC MonsterX already set up with racks.
From in the box to on the bike in about 5 minutes, no kidding. Rode 3 whole miles with ~5 lbs of risotto, a growler of beer and a bottle of grappa. Very rigid system and easy to secure and remove their bags. Yes, the fender is more novelty than functional fender, but whatever. I was concerned with bag to heel clearance since the bag mounts are not adjustable, but they cleared fine (size 50 shoes, 180 cranks and 425mm chainstays). Tires are 28 GP 4000s that run 31, so much larger tires would clear the rack.
Ultimately I am very pleased, both the rack and bags are extremely light and high quality. Without the bags I couldn't even tell the rack was there. My wife is looking forward to trying them on her 20 mi commute enabling occasional "fast" commutes on a road bike v. the hefty commuter.
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