Well - it turned out to be worth the swap - as it was New First... Hooray. Me and Mrs 747_not_777 had a lovely flight in 2A/3A.
Loved the new seating, the 'window and blinds', wardrobe, bigger screen for movies, seat controls, cabin ambience etc. All very positive and a throughly enjoyable experience with a good crew.
I'll now have to wait to see FT Dashboard update, to see if I'd have still got NF if I'd stuck on the original BA195...
As for the arrivals at IAH, it was perfect. Absolutely nobody in the immigration hall at all, the Border Secirity agent was even polite, welcoming and wished us a pleasant holiday (!), bags were out quick and the ride to the Avis rental desk was seamless and rapid.
All round, a big tick in the box for BA's NF and IAH. ^