Half price is really not a brainer. SU uses 330-300 on flights to Tokyo. These are showing normally 5 rows in J which means nearly flat seat. Hower, a day before departure you have a chance to see 5 rows swapped to 6 rows and 6 rows are older non-flat seats (same cabin more rows).
I cant advise though how likely this swap is for Tokyo route.
On the in-flight service it is really good, i would recommend to give it a try.