Whipping through the second page. No real problems, just a few observations:
I started with the Mobile Variant. The page is literally text area followed by image, repeat. So I made each section a Flexible Block as centring each object is what I want.
Moving to the Main Variant and I realised I would like to have some of the images arranged around the text area, as opposed to squarely above. I knew the following may well cause problems, but I had a go anyway:

I have FlexBlock with text, then FlexBlock with image, then another FlexBlock with image. My idea was to rip the two images out of their FlexBlocks and ALT drop them into the text Flexblock so I could arrange them more aesthetically. I was happy to leave the Mobile as is, but, since 23.8 there HAS to be the same blocks in both variants, so I was more than happy to have the Mobile arranged with all three items in one Block.

It worked, nearly. I dragged an image out, dropped it in no-mans land, then ALT dropped it into the FlexiBlock with the text. Checked the Mobile and the image is dutifully sat below the text. I repeated with the second image, and again, success.
I then tried to move and resize the images to where I wanted them in the Main Variant. Apparently, the ALT drop is a one-trick pony, the image was no longer free to roam around the FlexiBlock. I did some fiddling and messing and somewhere alog the way I lost the second image. Putting the second image back in created an identical copy in the Mobile Variant. I now have twins.

Not hard to recover from. In fact, all the problems I've encountered are easy to recover by simply deleting the Block and popping a new one in. Not something that can be done so quickly with a traditional site (I might change my mind when Layers are employed).

It would be nice if I could toggle between Flexible and Freestyle.