I have flown the 'old' but still very present C class:
i) Product is very "B" grade compared to BA
, etc in terms of seat (not lie-flat; higher density), but still slightly ahead of US carriers
ii) Service is either very good or mediocre
iii) Flights are often full and in this config it can feel like Y class after the above airlines
iv) Looking forward to trying the new J class, but have heard mixed reports, including IFE NEVER works fully on any flights
When all's said and done, there'll be more said than done.