I actually have extensive experience with the ZR products, having worked as a mastering engineer in 2 different rooms with ZR products for many years. Both the original ZR design which included actual construction of the room & an existing room that used the newer mountable panel version that is available now. One of the rooms was already constructed when I started working there, the other room using the modular ZR panels, I was involved in the design & built-out.
I also have over 2 decades of acoustic design experience & have designed & built around a hundred studios meeting many different budgets over the past 10 years using products from pretty much every manufacture available & custom built designs.
The original design, that included room construction was pretty amazing & probably one of the best sounding rooms I've ever worked in.
It also cost upwards of a few hundred thousand dollars to have that room built.
I can not say the same thing about the modular panel versions that are being sold now.
What I can tell you is that they are really good diffusors. But the diffused waves that come off of the panels still need to be absorbed to be truly reduced & controlled. And the 3/4" thick MDF panel does not really do much for bass freq's. If you understand the physical size of a single waveform cycle at around 40-60Hz that concept is silly, much less getting down to 20/30Hz.
Maybe if you covered every inch of all 4 walls & ceiling with the panels that also have the thin layer of absorber material over them you could get away with just using the ZD panels, but it would really depend on the dimensions of the room, how thin and/or solid the walls physically are, etc, etc...
When I was building out the room I had with the ZR panels it became evident really fast that we were still going to need to add some standard bass trapping & absorption to get the freq response to a point considered usable for a professional mastering studio.
In the end the ZR stuff did handle the diffusion well, but it also prob cost around 3/4 times more to get it there, than it would have just using classic methods.
And compared to what we paid for the bass trapping & absorption from other manufactures that was still needed after all the ZR stuff was installed, it was not really worth the cost & we have not used ZR products for any of the rooms that we've built since that one, if that tells you anything.
These were for mastering studios, not home listening rooms, which tend to be considerably different animals when it comes to acoustics & speaker setup & the aesthetics of the room after it is all done.
BTW, not giving my name here because I still work in the industry, so you can take this info with a grain of salt. This is just what was what my collogues & I found when working with the ZR panels & then having actually worked as a mastering engineer in 2 of those rooms for a over a decade.