I haven’t been in Blu on reflection but I have been, very recently, been in Blu on other S class ships. In my opinion Blu is a major step up from MDR in all areas, ambiance, service, food, everything. I find the food consistently excellent in Blu. I don’t know about the E class ships, however, if a true balcony room is important to you, you will not get that on the E class in AC.
The only other level that can eat in Blu are suites and only if there is room. Since suites have Luminae, I don’t think too many eat in Blu. We were on a full ship a few weeks ago and never waited for a table at 7:30.