ExpressVPN likely switches up their server addresses to avoid the GFWC. The only way to get a "reliable" VPN service in China is to get licensed which would mean handing over any encryption keys they may use there. You can often connect, but it doesn't always work, might take a lot of time or be subject to random disconnects as the packet inspection decides you're not authorized. In the past, I've seen a number of western vloggers, they usually hop across the bay to upload their material (still using a VPN). Those that do not usually go to licensed VPN providers. Again, a lot of this may have changed since the crackdown as they really don't want unrestricted news feeds to become prevalent in China ("for harmony purposes")

As I mentioned before, you could also attempt to use a corporate VPN if you have one (although that has it's own issues). You could set one up yourself if you have a router capable of it.

VPN software and a router are two different things. VPN software is hosted on your computer and initiates the connection to the target entry and exit points. A router is just an additional segment in that connection. I brought just a regular router when I traveled there (I still do if I'm traveling and know I can't secure a decent wifi signal), but those aren't the portable type. They gave me a stronger signal which the portable ones usually didn't. I could also set up my own internal network before I left the country if I needed one.

I can't speak for the current generation of portable routers, but any Wifi AC router should be more than enough for the standard hotel room (assuming you have wired ethernet... in the bigger cities, they may have switched completely to wireless).