What would dual Z axes on the mini achieve? The existing cantilever design is plenty stiff in my experience, I’m skeptical you’ll get any significant increase in print quality or speed, and I suspct at the cost of having to fiddle around a lot tuning settings to get it back to where it started as the existing firmware has a lot of tuning for the mechanical behavior of the exisiting design. So, if you’re not happy with the mini as is, I would be looking at a different printer rather than a dual Z mod.