Whether or not the dual centres are better will depend on where you sit and how much of the resulting comb filtering will be audible. Depending on frequency and where you are located the sound from the two radiators will be out of phase so accuracy of the sound will be compromised at other than the sweet spot. Listening even slightly off vertical axis of the pair will have audible effect. At some frequencies amplitude will be reinforced and at others there will be cancellation.
In some rooms such a setup conveys a greater sense of spaciousness, but I've always found the clarity of speech suffers especially as you move off the vertical axis. One way to visualize it is to think of a pond of water where two stones are dropped simualtaneously at opposite ends of the pond. Depending on where you are in the pond the waves will be of different amplitude.
If you are only concerned about the one sweet spot on vertical axis then such a setup can work, but don't expect guests to hear what you are hearing. Even well designed horizontal centres are a compromise and can suffer from some comb filtering, though the better ones have less of this problem. By aiming the speaker directly at the listeners, at least those in the front row hear more or less the same sounds because as you would expect a good horizontal speaker has better dispersion on a horizontal plane than a vertical speaker.
Ultimately you should try both to determine what sounds better to you, especially if you are just concerned about the sweet spot. The sense of spaciousness of the dual M22s may be worth the comb filtering. The best option is a single identical speaker as the mains on the same plane halfway between the left and right, though like most of us that's not possibe which is why you need to check out these less than ideal alternatives.
In my HT one of my objectives continues to be to try and get the same sound from all seats which is a daunting task and one more easily accomplished in the lower frequencies. Dual vertical centres sounded too different depending on where I sat and dialogue wasn't as clear so I opted for one horizontal centre aimed at the front row. One day I will likely go the perforated screen route and mount a single vertical in dead centre behind the screen. For now its the single horizontal below the screen.
