Took LHR-DEL in F this weekend, overall it felt like their J product with a bigger seat and possibly slightly better service.
Ground service:
At LHR, there was nothing differentiating it from J, no personal escort etc. The SQ lounge is closed so you're directed to the UA one.
At DEL there was a person waiting with my name, definitely made the Intl->Dom connection much easier with my massive bags.
(One group had a buggy and multiple people waiting for them, possibly because they were in a group?)

Seat:
It was an ex EY plane, while the seat itself was nice it was definitely old with parts falling out, doors being loose and sliding around during take off and landing etc. Definitely would be better when the A350s start flying.

Food & drinks
The bar menu was the same as J I believe, with Laurent-Perrier being served.
F has a separate food menu with a lot of options for the lunch main. The light meal is the same as J though, if not even more restricted based on the online J menu.

It was still the old soft product, amenity kits etc as i believe the new one launches with the A350 later this year. As of now, I don't think the premium over J is worth it for the prices they're charging.