I was in a very similar position when I was coming up through jiu-jitsu, with an awesome instructor who had a great deal more experience, even than Eddie Bravo, so there was some concern about this. Of course, he's also a Royler Gracie student, and those who know the history will note that there's some bad blood there.
I think that it never hurts to ask your instructor. Generally, they take it as a sign of respect that students opted to ask beforehand.
That said, I really do think that the Rubber Guard is not something that is really fit for people who are getting started in jiu-jitsu. I do know that a lot of 10th Planet academies teach it right off of the bat, but the reality is that it requires a substantive level of experience with the basics of jiu-jitsu (being able to break down posture, controlling the hips using effective distancing, etc.) in order to be effective. Those kinds of fundamentals are not usually present after six months of training.
Personally, my advice as someone who love the rubber guard posture control stuff (though I don't like the lockdown at all) is to focus on controlling your opponents' first. The place that you're at in jiu-jitsu really is about learning to develop the high guard in a way that is consistent and good at establishing control behind the head. As you start to feel more and more comfortable with that level of control, then it is reasonable to start getting a little more aggressive and stepping up to mission control. Once you're there, you can work your way up.
Hope that is helpful.
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