Joshua – it looks like the last gen was made in 2016, so these are fairly old for network gear and you may run the risk of the devices dying. There are 4 vulnerabilities ranging from 5-7.5/10 which is not great but the alternative below will help protect you.

The alternative you describe by placing a wired router that supports ExpressVPN between your modem and the airport extreme you could protect all of you devices with the VPN and still use your apple routers and airplay. This also protects your apple network devices from being connected directly to the internet, which would limit the attacks on the vulnerabilities they have.