My wife and I took advantage of the upgrade option on this flight back in April, I can only compare with Qatar J class. (Seats 14A/B)
The positives were that I found the seat very comfortable & spacious, I preferred it to the Super Diamond seat on Qatars B788 & A350, in particular the larger footwell.
Not quite as good as the Q-suites, however I also liked that as a couple you could be side by side with a window view, with direct aisle access.
We thought the food quality/quantity was better on Qatar & also the presentation on Qatar is so far superior.
We asked for the meal to be presented about 2 hours into the flight, as we had a breakfast in the lounge, but it appeared straight after take-off along with everybody else.
The cabin crew appeared to want the main meal service out of the way as quickly as possible & the crew were not quite as polished or attentive as Qatars cabin crew.
Also, the drink service was lacking somewhat,we had to ask all the way through the flight.
Overall, Qatar J is superior to Oman J, but with some tweaks here & there, would not be far behind.
Apologies for the quality of pics below, taken with my smartphone.
