Any idea and are these a decent throw?
Depends on the M1, there are two difference versions. One that use the older style One Drop pads and the other that uses One Drop’s standard Flow Groove Pads. They are an old school, undersized throw that have a great feel but are not as forgiving as more modern throws which tend to be larger and wider. They have been retired for quite some time now so you will have a hard time finding a new one.
The older one will fit 21mm pads, the other I’m guessing 19mm pads would fit if it’s just a regular silicone groove. I only have experience with the older version.