I've always been interested in an M tooth saw but never was around one. I recently saw one on Craig's list and picked it up. It is unused 5' Tuatahi Homestead model. It was razor sharp and still had the original rust protective coating. It cuts smooth and fast with no catching. I cut a 10" alder log with it and compared it to a vintage peg and raker saw. At a normal working pace and no real effort the M tooth cut through in about 30 seconds compared to the vintage saw at 45 seconds. The log was not real solid so it rocked a little and that would normally cause a raker saw to catch but M tooth was not affected and ran smooth.

In general these saws will cut faster then a traditional peg and raker saw in knot free wood. They may pull a little harder but not much. For me maybe the biggest disadvantage is that they may be stopped by a knot at the "wrong" orientation. It you look at how they cut they do a good job of cutting cross grain but not when cutting lengthwise as in ripping or hitting a lengthwise knot. In the photos below I show the results of a ripping test compared to a peg and raker saw. The peg and
raker saw rip cut much much better in the soft wood I sawed. With a hard knot I would not be surprised to see the M tooth stopped completely.

The saw is about 0.090" thick with no taper and quite stiff. From the factory the set varied quite a bit, it varied from 0.014" to 0.024" with most close to 0.017". The saw did start to bind a little on some logs so I changed the set to a uniform 0.020". I do not recommend setting just the tip of the teeth because at least some are quite hard and it would be easy to break a tooth tip off. With the set set to a uniform 0.020" it cuts free now.

I'll have to do some more comparison with vintage saws on different wood and sized logs.