A word of warning with the M Part one, I don't have a torque wrench and have seemingly overtightened it. My steel seat tube is no longer round.
I suspect this can happen with any clamp but this one specifically has "pinched" the tube where there's a gap at the bolt.
agreed, I just looked too. Apparently only 31.8 and 34.9 available. I have gone with a very basic M part one