You can install SlicerMorph in two ways:
Download and install the latest preview build of Slicer and then install the SlicerMorph from the extension catalog. This will install additional extensions that SlicerMorph requires as dependencies (e.g. SegmentEditorExtraEffects)
You can download a customized 3D Slicer for Mac and Windows from http://download.SlicerMorph.org. The additional benefit of this customized version that it is portable and can be run from a USB drive.
SlicerMorph specific functionality between these two routes of obtaining the software should be identical.