It's what the US system SHOULD be for US citizens. No need for interviews, extensive criminal checks, denial of US Passport holders/citizens with 30+ year old misdemeanor records or expungements and no other offenses of any kind, etc. etc. You're eligible for entry, you can apply for the Iris scan.

I've never had trouble at LHR, but the last time through Gatwick a few weeks ago it wouldn't recognize me (2 weeks prior it worked fine at T3 of LHR). That was just the first of a series of issues at LGW that trip (the worst was with their version of the line/baggage sizing dragons, but that's a whole 'nother story).

Funny that the UK Iris system works fine, but Clear could never read my irises so I'm set up with them by fingerprint.