I have concluded my initial useage of the ist holster type pocket pants.
They are actually very secure between the webbing type waist belt and the wide neoprene / Velcro leg straps. The pockets are secured by zippers rather than Velcro. I did not notice the pockets twisting like you would experience by a leg strap only individual pocket.
However, they suffer from a substantial storage limitation in comparison to xsscuba and the like pocket shorts. The pockets on the 1st holster pants are probably on 50% of the volume of the conventional pocket shorts.
Whether this is an individual limitation is another question. YMMV, but they are definitely too small for a wide 6 foot tech DSMB and 150 ft reel. A recreational smb and 70 foot finger spool is ok. A spare mask and defog is also ok.
I did find them very handy for carrying smaller items including tools and fasteners for work underneath the boat. They are also much, much more streamlined than conventional shorts which could be of interest to many.