Yeah, the turtle is more a historical thing than a good test. www.whatismyv6.com i think is the gold standard, the page loads fast and shows the address clearly. You can also go to sites like www.comcast6.net and www.arin.net and several other sites will reflect back the IPv6 address that their server received you on. Another good hint is that the address they reflect to you is from the T-Mobile USA IPv6 range which starts with 2607:FB90:..... If you see that you, know you are doing the right thing for sure.