About nlbwmon configuration for VPN


Say I have my local network on 192.168.20/24 and VPN Clients on 192.168.50/24
I added 192.168.20/24 and 192.168.50/24 as "Local subnets" in nlbwmon config tab
now should I also select vpn0 interface beside lan interface to get the traffic for VPN clients?
and should I select wan interface too?
Also is it really that bad for flash wear to bring up "Commit interval" to more than 12h interval
I'm using usb stick as a root overlay