

That sounds like pretty much exactly what we did at my last job, and it worked pretty well IMO. The individual commits in a PR didn’t ever matter. I don’t even think we used them for code review, except if it came up for review a second time after rework. In that case, we were able to just look at the new commit to see if the right changes were made.
And we definitely avoided basing off each other’s branches. We had to do it a few times. The only times it went well was when the intent was to merge the child branch into the feature branch. If they were actually separate tickets (and the second relied on the first) it was generally chaotic. But sometimes, it was just necessary.
The grooves?
The pattern on the left is actually just inside the case, under a clear part of the case. That part is black in the Euro version, but the case looks the same otherwise. (We have cases like that, too.)
Edit: Also, that Japanese one? I’m pretty sure it’s the same style, but turned upside down. That’s the base of the case. Searching Google, I found a copy on Ebay that shows the front, and that section of the front of the case is clear for that one, too.