One note to mention Amex doesn't seem to report a 30 day late until the account is actually 90 days late, does not mean I would be testing this!
Now this Clear Card it was good when it first came out because they were offering a 3.9% BT for LIFE... but as far as rewards go and paying late, you can get much better rewards and paying late on a credit card product with Amex a couple times is a great way to see a 10k limit come crashing down to $500 in a real hurry!
I inadvertantly tested this one December when I had a lot going on. Never saw a missed payment on my credit report.
I remember them charging me with a fee, but then crediting my account back.