I have been looking through the specs recently of the 150MLX and 150SA.
The 150MLX (which is cheaper) seems to have a better cantilever, and some would argue a better diamond profile. A certain amount of "design to cost" seems to have happened with the SA version with the use of an aluminium cantilever supporting the Shibata profile diamond. I have also read that the body has been tweaked so the AT150SA has more in common with the 440 than the 150.
All that seems interesting, but the most important question is how does the SA sound in comparison to the MLX? Has anybody seen any reviews, or have direct experience of the two?