I know several people that REALLY like the 9. Every now and then I think about switching but cannot justify the cost. Maybe when the 10 comes out.
Anyway, one thing I learned is the the Metabones adapter causes problems. It seems the Sigma adapter is better... no issues.
Then again, Sony lenses will work better on the Sony body better than any lens with an adapter.
I went with Metabones mainly because Sigma doesn't tout their adapter as being Canon compatible, which worries me as far as future updates compared to Metabones. Tony Northrup had a comparison against the Mark IV and the Sigma was softer in the corners. Also, I didn't see a whole lot about the new Mark V, with the exception of Ken Rockwell's review, so even though I liked the price of the Sigma, I had more of a comfort level with Metabones.
I should mention that some of the pop ups may have just been user error as I flipping through menus and changing settings. I need a book to explain some of the settings, to be honest. I looked into Gary Friedman's book (mentioned above) and it is only available via a direct download in pdf format right now. I did a search on Amazon and no one has an A7RIII book at this point, so I guess I will be looking through a lot of YouTube videos or buying the pdf version.
Personally, I was looking for more of a camera that did well with both video and photography and I liked the way the A7 handles both versus other options I looked at out there. Personally, I don't take a lot of photos this time of year (not a fan of cold weather), but I will put it through its paces in the next few months. As you said, Sony lenses will probably work better, but I don't know that I want to kick Canon to the curb just yet if they are 95 percent of the way there with an adapter.
One thing I did was pull my APS-C Sigma 18-200mm off my old 20D. I set the Sony for APS-C shooting and it worked like a charm. I couldn't use it on the MarkIII without having black circles around the photo. I have better lenses nowadays, but I used to shoot quite a bit with that old Sigma when I was on trips and didn't want to carry a bunch of gear.