I've never really given the F series much thought at all, but from time to time I like to research discontinued Mesas to see if I'm missing out on anything. I never really loved the Express, I just liked it, since they are often compared I figured the F series wasn't anything hadn't already heard. But the high gain tones based on various videos I found sound pretty impressive to my ears! It almost had a Fryette/VHT vibe, (which I always thought was a nice blend of Mesa and Marshall) and that's not a bad thing. I don't know if they seemed to only appeal to a nitch market or what, but I may have been missing out on something! Considering I have a Mark V I doubt I'll find myself purchasing one, however they do spark my interest!