I am using the AX700 in the Gates housing. Here are some random thoughts not necessarily in any order except that I just thought of them LOL
It's an improvement from the AX100 in a couple of ways.
First I think the autofocus is a bit better than the AX100. I also like the housing better since the screen can be tilted upward a bit instead of being fixed as it is in the AX100 housing.
Gates has added an extra latch for the two halves of the housing - not sure it makes a lot of difference. The screen is less cluttered since the pushbuttons have been eliminated from that location.
It uses the same ports as the AX100 so no difference there.
The white balance seems better for the AX700, although I can have occasional problems with it. Probably operator error.
I would have preferred a slimmer case with a small external monitor like some of the older Canon/L&M units; the AX700 can do video out while it is recording 4K which the AX100 was not able to do so an external monitor would be fine. I realize this might entail more batteries, not a desirable thing for me.
I like having two SD cards. No reason to need another card for a day's worth of diving especially if I use two 256MB cards.
Here's a little piece about collecting lionfish in Bonaire for a sample video. 1K with almost zero post processing: https://www.youtube.com/watch?v=VV68OLXgrF0