When I was looking to get a little more standardized and efficient with my diving, I asked many of the same questions, adjustable vs continuous - making it work for different exposure gear - steel vs aluminum plate - quick release - etc.
After doing quite a bit of diving, and a lot of gear tweaking, I have the harness and crotch strap on my heavy steel backplate set exactly where I want for ideal trim. I also ended up with an aluminum backplate with a different harness that I use when i'm diving somewhere warm in a wetsuit, and the length of the harness are where I want them for that configuration, and I wouldn't want to adjust those either or I'd need to dial it all in again. If you're only going to be doing one or the other, you'll never need to adjust your harness or crotch strap once you have them set for optimal trim.
Zero regrets, never wished I had buckles or quick adjusts.
After doing quite a bit of diving, and a lot of gear tweaking, I have the harness and crotch strap on my heavy steel backplate set exactly where I want for ideal trim. I also ended up with an aluminum backplate with a different harness that I use when i'm diving somewhere warm in a wetsuit, and the length of the harness are where I want them for that configuration, and I wouldn't want to adjust those either or I'd need to dial it all in again. If you're only going to be doing one or the other, you'll never need to adjust your harness or crotch strap once you have them set for optimal trim.
Zero regrets, never wished I had buckles or quick adjusts.