We're traveling from Chicago to Rome on 10/1 on British Airways on tickets purchased through American Airlines.
Both airlines ask to use Verifly for travel to the UK. Here's my experience:
1. Don't bother looking at Verifly any more than 48 hours until your flight. I found that both the BA and AA flight numbers/routes were not available before then. Within 48 hours, our BA flight number was available, but the corresponding AA fight wasn't. So, I used the BA info.
2. I filled out the UK passenger locator form. This is similar but different from the EU Passenger locator form which is required for entrance to Italy. Verifly has a link to UK form. After completing, it's uploaded by scanning a QR code. Note: There is a box for TEST BOOKING NUMBER. I have no clue what that is, but I google Ricksteves and a few people suggested using "none" It worked.
3. Uploaded a picture of the negative covid test
4. You'll need a photo and will answer some basic questions and that's it. I was able to add my wife's info on my record. All items were approved in about 60 minutes.
For travel from the UK to Italy, BA asked for the same information (EU locator code not the UK) and has a portal for the information in the Managing Your Booking section of its website. Very easy to upload and docs were approved almost immediately. It's much faster and makes more sense than Verifly.
…. At ORD, verifly not used. BUT it forced us to have all the necessary paperwork ready. Several travelers didn’t.
As we haven't traveled yet, I have no idea how the check-in experience will go. But at the paperwork is done. And we have several copies of everything.