Went through back on the day after Thanksgiving 11.28.19, used the Clear lines with TSA Pre in the United Terminal. No problems or backup,

Now, was in ATL (off topic) last Thursday at 18:00 EST and there were 100+ ppl in the CLEAR line. Line was entire clear line, parallel clear line and then jumped across the hallway to the regular check in lines and serpentined around for another 50 ppl. Didn't take more than 20 minutes to clear (pun intended) but still freaked me out for what may be to come with United terminals and all the FF promos.