That's looking a bit overfermented to me. The photo below (one of Norma's doughs) is about the furthest you want to go, imo.
In the past, I've made kind of a big deal about dough underside appearance, but I think I'm beginning to slowly move away from it. It definitely doesn't hurt to monitor it and get a photo, but if you ferment a dough for a couple days or more and achieve the right volume (between 2x and 3x) before stretching, the bottom appearance will work itself out just fine.
One advantage to underside appearance is that volume growth can be a bit tricky to detect and if you're posting photos online it takes photos of the starting dough and finished dough to determine growth whereas an underside shot can tell the whole story in one photo. Other than that, though, there's nothing wrong in going strictly by volume.