And companies that deal with acoustic treatments use a bit of science and engineering. Reputable commercial acoustic treatment manufacturers do something called lab testing of their products and publish the data so that the buyer has an opportunity to evaluate the efficacy for their acoustic issues. All these materials have a range of effective frequencies, yes, even foam. The question becomes, how wide a range of frequencies do you need to solve your fundamental problems?
Seems to me anyone who builds a studio space is recording and mixing audio. It seems rather obvious that one should have a basic idea of audio spectrum in applying EQ and mixing various sources. I'm trying to gently ease into this question. How did you determine what frequencies you need to treat for in your studio space? How did you evaluate these two products, at the thickness you used, as to how they would perform?
You say you were disappointed. What were you expecting, magic? I know I'm walking a line where I could come off as being overly harsh. Sometimes the most obvious problem like flutter is masking other issues. Many who have been through this know the rabbit hole it can become. Yes, for some it can be a little overwhelming.
This is homerecording.com where gathered are those who desire to be musician, songwriter, producer, engineer and for many, at least rudimentary studio builders. If someone told you that if you want to be a songwriter, that it requires effort to learn the craft, most would have no issue with the advice. Is it not the same for those who wish to acoustically treat their studios? If I say you probably want some basic understanding of the problem is that too heavy an ask? DIY can yield great results but that is totally dependent on knowledge, otherwise you are depending on just dumb luck.