No other reason than once the tunnel was established, and rather than trying to include a CF Origin Certificates into my server (& other stuffs), it was just 1 command away to get a certification (it's where I last left off following the guide).
I did read about the difference between CF SSL & LE, but I don't have a full understanding if LE was necessary or not in my case.
The Tunnel was established in my Proxmox VE's Cloudflare LXC, rather than the VM which hosted the Mastodon server (if that's an option). And I figured if in the future I make more VM + servers, then this current tunnel should take care future port 80 & 443 issues.