I just flew in 16F on a 757 (BOS-SFO) and I have to say I was actually very impressed. Usually I like rows 8/9, but since the flight was full and I booked at the last minute, 16F was all I could get. Much more legroom than normal E+ seats, full recline, and two windows to boot. The armrest was not built into the side of the plane (but in row 15 it is), however it is definitely shorter than normal. I'd say it's about half as long. I didn't really have any major issues with it, though.

To answer your question, the armrest does not move up, since the seats are so much further back from row 15, the tray tables are in the armrests in row 16. Not a bad price to pay for the legroom, though

My one complaint was that as we landed, I got a nice shower of condensation from the top of the window. It was a bit chilly, too, as there is some air leakage from the door seal.

But overall, 16F gets ^ ^ .