I've got the Sony G series 10-20 PZ. Optically it blows both the 10-18 and all the kit lens out of the water. I've yet to dive with it, but have it's zoom gear on order with Reef. My only port on my a6500 rig is a modified N120 4.33 mini dome with a Port 72 macro swing mount grafted onto it's shade wings. I've moved to N120 with the 35mm N85 to N120 adapter with focus knob. The 4.33 works very well with my Zeiss Touit 12 and reputed excellent Canon 8-15 FE using a Metabones IV adapter. I use the Canon glass either solo or with a Kenko 1.4 TC, a popular combination for extreme CFWA. The ultra sharp Zeiss 12 worked well as a rectilinear in the 4.33 FE mini dome with the corners being ever so slightly less sharp, as compared to the larger 7" dome, but barely noticeable, and certainly not worth giving up the size of the 4.33 and Close Focus Wide Angle (CFWA) capabilities, which were astounding. Moving to the Canon 8-15 was an even bigger leap in IQ. Love this Canon setup for maximum IQ ad CFWA versatility, but it weighs a TON with the Metatbones, Kenko 1.4 and heavy Canon 8-15 glass. Nothing near as heavy and bulky as a full frame, but certainly took the light-weight travel rig reputation of APS-C away, at least what I was used to from my NEX7 days.
Okay, getting back to the original inquiry and the Sony 10-20 PZ. This tiny lightweight power zoom is super sharp throughout it's range, even wide open to the corners. It also has an extremely short minimum focus, since it was primarily designed for blogging. It's a G Lens and superior to the 10-18 and 16-50 optically. On land, of course, it all looks great through the 4.33. Underwater the Zeiss Touit 12 worked well in the 4.33 mini dome, so I'm curious if the added 2mm of WA will work as good as the Touit 12, or better, especially since it has even closer minimum focus. The Sony 10-20 PZ should be a killer for CFWA and be a very lightweight travel rig, compared to the heavy Canon 8-15. Given the popular increase in underwater video, it's PZ has many advantages, along with it's lightning fast focus. I use it with my sensor stabilized a6500, so it's lack of optical stabilization is not a hinderance.
The 4.33 is a versatile dome because it's slightly bigger than the popular 100mm and worked well for grafting the Port 72 swing mount onto it's shades to make it a FE, WA and M port all in one. This setup, along with a 20 and 30mm extensions, has allowed me to shoot the Sony/Zeiss 16-70 for moderate WA and SM (single dive setup when I'm unsure of my target) , the Zeiss Touit 12, the Canon 8-15 FE/Kenko 1.4, along with the Sony 90mm macro (plus many more)....all with one travel friendly mini dome.
I'll be diving in the Philippines this year and will post the results with the Sony 10-20 PZ and the 4.33 port. I may do some underwater focus testing in my hot tub just to see what the results in the corners will be before the trip.
Marsh
for now I'll stick with the 16-50 with the WWL-1B and CMC-2 see how I like the optical performance. Hope to be the same or similar as 28-60 on my FF A7RIV rig I downsized from. 
