ahrgh, modX says :
Dual Compatibility
they are nuts, they know it's not 100,00% true
so i personaly like the old-new amxmod stuff more, they seem to handle the 3-versions stories bast AFAIKS.
/and they _do_ put a usable release up, e.g. including the most widley used modules, while the modX guys send you to search until you got i working