I played around with a Customizer beta a long time ago.  I was looking to use the Victoria 2 mesh.  I found it very difficult but got it to work.  However the V2 mesh was so poorly designed I could never get it to look like anyone.  I think this is also the reason Poser faceroom doesn't work.
Since then I've always exported the facegen head into Poser and put up with mismatches at the neck join.
V4 has a better designed head mesh so maybe someone can Customize it.  For me, life is too short.
I heard from Andrew at Facegen that they were working on better integration with the Daz figures and that something might be coming out in beta about now.