In SRM 1.3 it was a feature improvement to go from a main plus guest network to an additional three extra networks. I don't have much experience with consumer/home routers and if what others support VLANs, but I have experience with business grade appliances (Check Point, Fortinet, Palo Alto, Cisco) and, yes, they do offer more features: they also cost significantly more and above firewall and network features they usually require ongoing subscriptions. So for a home and small business that has modest networking requirements, I think the Synology routers offer a reasonable set of features. What would you use more than five private networks for? I find I can live with three: most devices are on the primary; IOT; guests. I have a fourth that I play with using WPA3 Enterprise authentication.
When calculating performance to size an appliance we would consider all traffic bandwidths across the firewall: WAN to all LANs; each LAN to each other LAN. So potentially the firewall has to handle multiple gigabits, since LANs can run at gigabit speed vs the WAN that was often a throttle. It's best to limit the use of protection mechanisms, which is why devices on the same private network only use the switching features. It's also why I place a managed switch in my mesh back haul: so the WRX560 mesh router doesn't 'trombone' its wireless client through the primary RT6600ax router's LAN port (two passes) to get to the wired devices.
I use load balancing on my DS1520+ to provide increased access for multiple clients: adaptive load balancing will work with any switch without further configuration.
When calculating performance to size an appliance we would consider all traffic bandwidths across the firewall: WAN to all LANs; each LAN to each other LAN. So potentially the firewall has to handle multiple gigabits, since LANs can run at gigabit speed vs the WAN that was often a throttle. It's best to limit the use of protection mechanisms, which is why devices on the same private network only use the switching features. It's also why I place a managed switch in my mesh back haul: so the WRX560 mesh router doesn't 'trombone' its wireless client through the primary RT6600ax router's LAN port (two passes) to get to the wired devices.
I use load balancing on my DS1520+ to provide increased access for multiple clients: adaptive load balancing will work with any switch without further configuration.