Premium Economy is instantly confirmed on NH, requires the purchase of full Y fares.
On the 777, Premium Economy seating is 2-4-2 versus 3-3-3 in regular Economy. More legroom and has a leg rest. I think it's superior to UA's Economy Plus. Food service is the same as regular economy, however of high quality. Now, if you can get UA to instantly upgrade you to C, then it's a different story.