Don't know what's going on with FR's checked baggage fees at the moment. Seems to vary from pretty much every route on every month.
That said they do seem more reasonably priced, especially 20kg bags which now seem more competitively priced compared to 15kg bags (previously it were always much better value for 15kg).
Looking from just a few random selections...
East Midlands to Rome-CIA, March 2017... 15kg=£14 or 20kg=£20 (one way)
Stansted to Girona, May 2017... 15kg=£15 or 20kg=£21
Manchester to Dublin, January 2017... 15kg=£13 or 20kg=£17
Edinburgh to Gran Canaria, July 2017... 15kg=£30 or 20kg=£39
Glasgow to Stansted, February 2017... 15kg=£15 or 20kg=£20
Birmingham to Bratislava, August 2017... 15kg=£20 or 20kg=£26
As I say, not sure what the full theory is behind these... but certainly not what we were led to believe only a few months ago where there was going to be just six different fees.