Being Canton my guess is that what they can do, they will do well, within their limitations. But...
Those F-251's are a bit similar to a pair of GL-260's that I have. Smaller woofer but ported with a larger cabinet. About the same specified bass response. I'm using the GL-260's in a room that is about 10m², so half the size of your room. They do a pretty decent job of filling that room with quality sound, with better sounding bass than their specs of 42hz would make one think. But that system is never called on to play really loud, just moderate levels. It sounds very good in that role with those limitations.
For low level to (at the most) mid-level or for background music in a room twice that size I think that the F-251's would be ok, but I wouldn't want to count on them for my main system or serious listening in a room of 20m². I would be looking for something larger for serious listening for a room of 20m².
Cheers,
James