Don't get the D3/Zenith combo.
I was a dealer for ten years and was in the first group of HOG dealers.
Attended one of the 1st HOG reg tech instructor classes at DEMA in 2011.
I wrote the 1st draft of the D2 and D3 manuals for HOG and the service procedures for a couple of the Edge regs.
I have always preferred the Classic over the Zenith. The Classic's purge cover is more user-friendly. Especially if diving with any kind of glove over 3 mils thick. I had several Zeniths, and as soon as the silicone classic cover came out, I converted every single one of them. And I tried to discourage my customers from going with the Zenith as well. I haven't looked at prices since I retired but I could also sell the Classic for 20 bucks less than the Zenith and my customers appreciated that. Just looked at see that it's like 10 now.
The Zenith's cover requires more detailed rinsing. I feel the Zenith cover is a little more fragile as well.
I certified over 50 HOG reg techs, divers, and shop techs before I retired from teaching in 2022.
If the person setting it up knows what they are doing, and takes the time to do it properly, they breathe as good as any reg out there.
Parts are easy to get.
I always got good life out of the 1st stage seats because I broke them in using a 3 step process. My average 1st stage seat life was around 300 dives with some going as long as 450. 2nd stage seats I replaced about every 150 dives. They are a softer material so that was expected. It is critical to store the regs with the adjustment knob set at the easiest breathing position. And with the micro-adjust they have, it;s easy to extend seat life without risking cutting a new groove in the seat because you are not turning the orifice.
And I always recommended going with rubber hoses. Cheaper and better value. As well as longer life.