Took a chance and tried it, but unfortunately it doesn't work at all on mobile. I can create a group name... Aaaaand that's it. I can't add any tabs to that group. And clicking the button to open a new tab into a group results in a button click animation and literally nothing else.

It keeps saying it saved 1 tab (chosen at random, apparently, since it said this even without me selecting any tab) but it didn't actually save any tab, and I certainly can't add multiple at once. No "saved" tab(s) appear in the group list.

Edit: gave it +1 star because I do appreciate that it only requires browser tabs permission. So many extensions grab more permissions than they need, but this one seems honorable/respectful of user privacy, and with only the browser tabs permission I think it is very unlikely to be fishy (even though it's broken for me).