No difference, the b is a little used suffix added to the WFP, theyre exactly the same, there is of course the 2407 WFP-HC which is the high colour gamut version of the 2407 WFPB, i would avoid this at all costs, the colours were far, far too strong and professional calibration equipment struggles to rein it in, the WFP used approx a 72% colour gamut but the WFP-HC used about 96% and was massive overkill.
Bet youre even more confused now.