haven't seen them mentioned much on here. FN dropped the ball getting them out to public by years, and I don't think there is much support like some other brands out there.
with that, unless you are getting a smoking deal, maybe look at one of the more widely supported platforms for multi cal. (AI,DTA,Barrett,) Tubb's new platform as well (bolthead changeable) (Cadex Kraken possibly soon). KRG SOTIC out soon also. AI, DTA, Cadex, KRG have reps on this board, haven't seen anyone from FN, even on FN forums available. probably missing others as well.
the switchable bolt heads are common place nowadays, again though, not a lot of FN support out there. Mausingfield and Bighorn have switchable bolt heads, probably others as well for custom actions. With new WTO lug and Mausingfield Barlok coming out, almost any platform can change barrels without removing action from stock/chassis. (Mausingfield and Bighorn founders are board members here)