Wider is useful in a bait ball. Sometimes u have to shoot down and sometimes theres no light to speak of so the 2.8 was used for sure.  In brighter conditions it might be ok to use higher fstops. I guess ill play it by ear.  I did try the 8-15mm canon but found it wasnt able for the dark conditions and abondoned it one year. 

To be clear, im using a7r5. Choice is just with the lens setup. I guess u helped answer my question, ill pack both!  Only thing the wwl cant do is split shots but not many opportunities for them in the fjords anyway. 

I prefer a hand strap on the side of the shutter release. Not sure if it's possible on a AIO housing.

Well they did have a few new items but a Z330 replacement was not one of them. Inon has never had a booth at DEMA to my recollection so if a new strobe arrives there it will be displayed through retailers at the show. 

The WWL has slightly wider coverage compared to a 16-35, something like the same horizontal field as a 14mm rectilinear, but the advantage for low light is you don't need to stop down as much with the WWL where you should be able to shoot at f5.6 or so.  I imagine corners will be dark water though - what f-stop did you use with the 16-35 previously?