I have no doubt that there will be some "bumps in the road", as there always is for something on the bleeding edge, but I jumped in at version 3.1.2, with FF6.2, and I've not had any problems at all, thus far.
I stuck with the ESR until a couple of days ago, when even its latest version (finally) became incompatible with the legacy Tab Groups addon (may it "rest in peace"). That's when I discovererd STG, and decided to "move back" to the mainstream FF release, and see whether STG would get me close to where I wanted to be, as compared to the original.
I am EXTREMELY happy with STG. There is obviously a tremendous amount of work behind it, and it really shows. I could NOT be happier at this point, with the result. THANKS for taking on this development effort, and "saving" all of us who felt like Tab Groups was one of "life's necessities". STG is a worthy successor.