We used them a while back for a portion of a run that happened at sea, they worked ok.
1). if the team wants armor they need to get the armored diving suit from R&G, no way are they wearing a standard armored vest/ jacket underwater...ha!
2). firearms do not work underwater (look up the mythbusters episode) so that means exotics like spearguns, gyrojets etc.
3). If any your runners have skillwires installed they will rule as they can just slot a chip and be able to dive like a pro and use those underwater exotic weapons.
4). Matrix will not work underwater, it blocks all radio traffic after your're more than a few inches underwater. No smartlink bonusess etc.
5). Astral projection under water is mostly useless due to visibility being blocked by tiny marine organisms (plankton, zooplankton etc).