I like them
I flew Economy Comfort AMS-YVR (777) and LAX-AMS (747), and must say the seats are more comfortable. They are different seats from the normal Economy seats, but it's not a different class (i.e. the service is the same as for Economy), but you have a better recline angle, and more leg space. Especially in all planes except the 747 it's brilliant, because they have the same personal IFE as business class. 747 unfortunately still has an overhead screen in Economy... But I did manage to get a good 8 hours of sleep in Economy Comfort from LAX, and I almost am never able to do that in Economy (am 6'7"), so even if I weren't FB PE (so it's free for me), after experiencing it, I guess I would seriously consider paying for those seats.