If You were to create two new groups one containing all trip weapons and the other all disarm weapons; Do you think they would be both balanced and in-keeping with a CRB (& Bestiary of course) only game?
A resounding "who cares"!
Oh well, I think it's fine but the only other DM I've asked thought they overlapped with the Flail Group too much - so why would you take Flails?
A bit like Spear and Thrown Groups I suppose.