This may be of interest to get a sense of the characteristics of how the different Vandoren reed models are cut:
https://vandoren.fr/en/reeds-technical-elements/
I had noticed that the ZZs seem lighter than V16s of the same hardness (a ZZ-2.5 seems lighter than a V16-2.5). This may contribute to the buzziness that littlewailer and AllenMouthpieces note above as well as what Jazz House commented, "they respond quickly and aren't too resistant. The main drawback is durability." The "reed comparison chart" at the bottom of the link suggests that both the green Javas and the ZZs are comparatively lighter than the red Javas and the V16s.
If you look at the four "jazz saxophone reeds" diagrams, the arches drawn on the reed diagrams on the left give a sense of the different cuts. It looks like the Java greens, with flatter arches drawn, have the least thickness difference between the heart of the reed and the side bevels. The ZZ seem to have slightly more difference while the red Java and V16s have the most. I'm interpreting that to explain why the green Javas and ZZs are lighter on the "reed comparison chart."
I'd guess that those thickness differences between the heart and side bevels contribute to the buzziness and brightness of the reed (a comparatively thicker heart stopping the buzziness), as well as a comparatively thicker heart being more comfortable for a strong embouchure, and reed with less thickness to the heart compensated by more on the side bevels being more comfortable on a more relaxed embouchure.
The 3 reeds at the top show much stronger arches drawn suggesting bigger differences between the hearts and side rails. The thicker hearts presumably relate to the darker sound of those 3 models, and stronger articulation compared to the "jazz saxophone reed" models.
I may have to buy one of those sampler packs of Vandoren reeds to try this for myself. FWIW I very much enjoy the ZZs. They are not as bright as the Rico Royals, and have a bit more spread sound. I find them easier playing than the V16s again with more of a spread sound.