It's there … for everybody now!
Grab your FX Composer 2 beta copy!
I already played a bit with Mental Mill some time ago … but only very shortly. The GUI seems a bit unusual (and a bit slow), but of course it's the first iteration and of course it will take time to learn how to use this tool. It can export to HLSL and CGfX. FX Composer 2 also supports COLLADA FX (Model Data and Shader Data) … everything very interesting.
I am curious, let me know what you think about Mental Mill and FX Composer 2!