The mechanism to move the arm rest towards the unoccupied center seat is located underneath the armrest and is somewhat tricky to operate. You'd have to be pretty wide for the extra 2" or so to make the seat more comfortable. Since the arm rest moves from side-to-side, it does not move up.

There were no regular Economy seats left when we booked our recent trip, so I don't know what the price difference is, but I would not recommend paying much/any extra for these seats, at least on the plane we were on KEF-BOS.

We flew WOW to Iceland from BOS and Icelandair on the way back, and found the WOW Xtra seat to be far more comfortable and well worth the extra $68. There's an extra inch or 2 (at least) of legroom on WOW vs. Econ Comfort on Icelandair, and no electronics boxes underneath the seat in front of you to limit leg/foot room.

I sat in 10D on the Icelandair flight, and there was barely enough width underneath the seat in front of me (9D) to put my 2 feet due to the IFE electronics box and the holder for the TV for 9D (there are no seats in front of 9D, so the monitor is stowed under the seat). Since the middle seat was unoccupied, I was able to angle one leg under 9E.

Also, avoid 9D, as the emergency exit slide protrudes significantly into the legroom for that seat, and the lav is in front of you.

We were able to preorder a meal in Economy Comfort, which ended up being the same meal offered to "regular" economy, just served before everyone else. and it was by far the best vegan meal I've ever had on a plane. On flights originating from KEF, Icelandair uses meals from Glo restaurant in Reykjavik, and it was fantastic.