Scandium is a metal added to an aluminium alloy to improve the alignment of the metal grain, and thus provide a stronger material allowing thinner walled tubes and thus reduced weight.
It's certainly true that early scandium frames were very brittle and failed (Dynamix being a prime example of this), but this was more due to over-excited engineers pushing the material too far.
I know people with Scandium Kona hardtails that are still being ridden after eight or nine years now. Most of Kona range is now build with Scandium alloy.
M2 was something special, it was a real metal-matrix material through the addition of ceramic. The M4 and M5 frames were merely a fancy alloy, costing far less to produce.