Hi Jean - as PharmDawgg said, from a DumaOS side, everything will be the same. It's not like a new console release, both the XR500 and XR700 will have the same feature set and level of support.
The difference comes down to hardware. Both are very powerful routers, so you will get great WiFi range and speed no matter which one you choose. The XR700 just has even beefier hardware as well as a Plex Media Server running on it.