You've read enough here to know that OCLP-patched Macs are not "set it and forget it." They still require work to maintain. If your customer isn't savvy enough to install OCLP on their own, they're not savvy enough to maintain it after you sell it to them.
I'm interested in your thoughts - why do you believe that selling your Mac with an unsupported macOS version (unsupported by Apple) is more valuable to your customer than selling it with its last official version of macOS and allowing the customer to upgrade with OCLP if desired? You could include a link to this thread and to the OCLP Documentation when you sell the Mac.
In my opinion, "Safe and reliable" needs to be your customer's decision, not yours.