Could I ask about Gatwick, separate tickets, and connections to Shetland after a TATL flight?

My traveling companion is flying in on the JFK-LGW flight, with a scheduled arrival at Gatwick at 10:00. He'll be in CW, and can do only hand baggage if it will help. Would he be able to make the 12:10 LGW-EDI service (BA 2940) in order to connect to the Loganair EDI-LSI service (17:45-19:10)? It seems to meet minimum connection times, but in practice, would this be a good idea? This fare appears on ITA, but is not sold on BA.com, which is what gives me pause.

BA.com does offer several options from LHR connecting to the same EDI-LSI flight at 17:45. I plan on taking one of those, as I'll be arriving on an earlier flight to LHR, and then the idea is that we'll meet up in EDI. I understand that the Loganair flight, booked in conjunction with the BA flight, will accrue TPs and Avios and also count toward the 4 BA segments needed for status. Would that hold true also for the LGW-EDI-LSI routing?

The alternative is that he does the airport switcheroo, and we both take the 15:15 LHR-EDI service together (or that he switches his TATL flight). But if the LGW-EDI leg isn't a bad idea, that would seem to be the easiest way to get us north as quickly as possible.

(And I'm happy for Shetland-related recommendations, too, although that probably belongs over in the UK destinations forum...)