Heh! I have always been facinated by anything assocaited with Lt. Co. Fairbairn so when Boker came out with their Smatchet, I picked one up. It definetly is a big, heavy knife and not well suited to quickly flick around. I'm no knife fighter, myself, but I think in a duel against an trained opponent with a smaller, handier blade you probably would be at a disadvantage. I don't think that was what it is designed for, however.
The Smatchet is a big knife for chopping and disembowling that would probably reward strength and agressiveness in place of skill and speed. In real life, using a knife in moden warefare is probably infrequent enough, that knife-on-knife fighting is almost vanishingly unlikely. In the sort of rough-and-tumble CQC combat against pistols, rifles, etc, I think it would probably excell. After all, the designer was one of those who had "seen the elephant" and designed the knife based on real-life experience with armed and unarmed combat.