Is it the same as Accelerated swiss? I remember that it was applied in Cappelle la grande chess tournament in France as the number of players exceeds 700...
I think its a very good option to play tournaments with these systems, I agree the mismatches really annoying.
An accelerated Swiss is designed to reduce the number of perfect scores and the acceleration is turned off after the second round. I've had a number of people want accelerated pairings because the round one mismatch is avoided, but it comes back in round three for the middle 3/4 (not quite as large of a rating difference) and the rating differences in rounds 4 and 5 (for the middle group) are larger than without accelerating. It sounds like McMahon keeps that acceleration on (think of a 7-round tournament using a pairing program where the tournament is set up as a 12-round tournament with the first five rounds being used to set the zero/half/full point byes to do the McMahon differentiation.
I'd figure that most tournaments large enough to use McMahon might also be large enough to be sectioned (in the US most organizers either allow playing up one section or have sections with overlapping rating limits like u1400, 1200-1599, 1400-1799, 1600-1999, 1800-2199, 2000-2399, 2200+ which allows a 1603 to play as a bottom rated player in 1600-1999 or as a middle-rated player in 1400-1799).
McMahon is far better.