Agreed, this has been my experience as well. Appreciate you mentioning OpenDNS, will look at managing the WiFi access with that. Given your experience and recently getting a blocked message on my daughter's phone when she tried to get to a haircut place, GreatClips.com for me. I have doubts about this tool's usefulness, if the filter hueristics cannot be augmented online with whitelisting websites obviously NOT adult content.
I ran into the same issue with adult sites last week. FOUND SOME REALLY big loopholes. Any luck with reporting it?
Have you tried either Gentech or Netspark on the devices? I did set up Gentech on one that was being used overseas (not via tmobile), and fortunately my child was honest about the loopholes. I spoke to Gentech and told them it would help if I am the admin, so they do not unblock any sites the child requests without my verifying that they're OK. Also, the child found a way to get to YouTube, although we had blocked the app. Next I'm going to try to have them set it up without any browsers, just preapproved apps, and we'll be watching for any access to the web via apps.
Would be very interested in trying opendns on my home wifi, since the k9 software I have on the laptops is only so-so.
I found the exact same problem, had my sons on teen, tested it and was easily able to get to porn sites