The way there advertising it, maybe a great idea most comfortable flight to Israel, to be able to fly LY to LHR and then LHR JFK.
It's been many years since I connected at LHR, and that was BA-BA. It is a huge airport, and if a terminal transfer is involved that's not fun!
I am not one to shun connections and have connected in IST (including the new one, which is much nicer than the old one, but is best done with a wheelchair assist requested), MAD, ZRH, GVA, FRA, WAW, SVO and YYZ. There are airports I would definitely avoid for connections, and LHR would probably be one of them unless there was a really compelling reason to connect there.