24 pounds is a good weight for a XC hardtail. Any idea what fork it has?
I don't know anything about M2 specifically. Presumably, its an alloy like the M4 / M5 which is designed to improve how the metal is worked with. That is, after welding it won't lose as much strength.
This is from the Specialized page on M4
The highlight for frame building purposes is M4's modulus of elongation, a measurement of how much shaping a given amount of material will take before it tears apart. Gram for gram, the M4 has almost twice the tensile strength of 6061 aluminum. It also has exceptional fatigue strength. And the basic density is equal to standard aluminum's-so it's plenty light.