The only DeSantis "Nemesis" holster I am familiar with is a pocket holster, synthetic matls, and open top.
I have one for my M36 J frame, and it is great for the price.
As far as IWB holsters in general, I prefer an open top IWB...My gunbelt on the outside, and my belly on the inside keep my pistol or revolver in place.
OWB, I do prefer some type of retention, like a snap/thumb strap.
MW