Hey! I saw your comment a while back but didn’t have time to address it at the time. It just popped back up in my head recently as I have been playing with my MC and MCMO and enjoying comparing how they differ. Note: I am planning to do a little write up about this soon to provide a comparison of the two, from my perspective.
Edit: This review is now up: Markmont. Classic Magnum Opus vs. OG Markmont. Classic
-About the OD GZR: These editions were from when OD was beginning to make yoyos out of 7075 aluminum. You can read more about it here: http://www.highspeedyoyo.com/reviews/n-z/one-drop-yoyos/one-drop-gzr-line
Essentially, the GZRs are the exact same yoyo design, but machined in a denser aluminum, and are heavier than the original 6061 versions. From what I understand, this is also comparable to how G2 does AL7 versions of their yoyos.
From there, OD optimized redesigning a yoyo to take advantage of the unique properties of 7075 aluminum (higher strength and density) to provide a yoyo that is similar to the original design but altered with a tweaked weight distribution that provides a new throwing experience. Despite the higher density of 7075, these versions can actually be similar in weight or lighter than the original, and will often have more rim weight. Examples: the Kuntosh 5000qv, Seven Summits, Legendary Terrarian, and the Markmont. Classic Magnum Opus.
Edit: As stated on the Legendary Terrarian page, OD now refers to this procedure as “boosted.”
In my opinion, optimizing designs to make the most out of the unique properties of 7075 aluminum is now a signature specialty of One Drop. They do it very well.