Yup, the Neilpryde High Hook Vest and NPX Immortal are essentially the same vest. The main differences, as you mentioned, are the graphics and the pocket in the front of the Neilpryde.
Most of the schools we work with use these vests for their students, and we've had overwhelmingly positive feedback from them. They don't ride up because of the harness hook hole, they have plenty of flotation, and they're so adjustable that they come in two sizes at once (ex. XS-S, M-L, etc.).
I use one when I'm racing offshore and I hardly notice it's there.
Hi I am on the heavier side and have been trying to source a Neil Pryde high hook in xxxl.
I seem to get the impression that they were primarily supplied into the U.S.A. market or just not made anymore .