When troubleshooting connection problems and changing router settings one at a time, with each setting change requiring you to knock the entire network + everyone offline including yourself for 15 seconds every setting is more than a minor inconvenience, its just aggravating to everyone on the network and can result in data loss if it reboots at an inopportune moment.
My problem was that the NAT Endpoint Filtering setting overrides Port Forwarding, and overrides DMZ settings. Completely! If I hadn't recalled a bit I'd read from an Ars Technica article explaining NAT functionality in regards to IPv4/IPv6, I'd have never known to try adjusting the NAT Endpoint Filtering to get one of my programs to actually work. Which was another + for the old Linksys that didn't need DMZ or port forwarding for the same program.
SMC Barricade... if you ever review one, try putting a P2P load on it. The last Barricade I had would actually crash with a mere hint of a load. Their tech support did have me try a few configurations, but that didn't fix the crashes. They RMA'd it, but even the replacement unit did the same thing.