ExpressVPN is a virtual private network. Its own site describes Lightway, a protocol it built, and TrustedServer, which wipes a server’s data when that server restarts. It also sells the Aircove router for a home network. People use the app for private browsing and for streaming.
Apps are offered for common phones, computers, browsers, and some routers. One subscription can cover several devices at the same time. ExpressVPN states a 30-day money-back guarantee on plans it sells itself. Server locations and which apps are included are listed on the ExpressVPN site, and those lists change.
Where this page shows an Up to cashback rate, that rebate is from KPON, not from ExpressVPN, and it follows the terms above.