I too was there today and had a sit in the first class seat. It went flat etc and seemed fine, but if it was an accurate representation then give me J any day.
The little leg room available immediately in front of you was quite off putting to me.
I have slept quite well in the A330-200 J not quite flat bed and will more than likely do so on the 747 J not quite flat bed again next week.
Yes I could see many people taking J with the comfort level it will offer. Not that taking F on my dollar will ever be an option so sleeping well in J will always be welcome.