Hi @stephenmillard . I don't know how a second subnet might work.
You could try setting up a "guest" network. There are instructions in the manual for the Archer VR2100 (not VR1600). The guest network can be restricted to just one of the bands, would use security as normal, have a simple wifi password, no access to other guests or your local network, would be subject to QoS-low priority.
Enabling QoS might affect your down and up speeds on your main network. Test before and after.
Reduce DHCP lease time, maybe to 1 hour, and even increase the size of the dynamic pool. Depends on how many customers you get and how long they stay.