If you tried it on a PlayStation then it's geolocked.
Working out which Sentai BD is region free is actually more complicated now. The Sentai discs are geolocked and a majority of the players are set to United States. All current consoles are geolocked as well.
The fact it works on my BD player is what makes it A/B. Chuunibyou doesn't work at all on that player, for example, despite it being Region Free, yet works on my PS4, so the fact that it works on both my BD Player when set to Region B as well as Region A and my PS4 makes it A/B.