I thought this would be a work around since you don’t have to be on the same network to use the guest mode feature. It did work to a point, as in I was able to log into Netflix, saw the streaming icon, and connected to chromecast as a guest within Netflix. But as soon as I hit play nothing would stream… The chromecast Netflix screen appeared on my TV saying ready to stream, and the play bar on my Android came up but the video wouldn’t play… I’m not super tech savvy but if anyone could answer this and or help I would greatly appreciate it. I just got my chromecast yesterday and still figuring it all out 
I use SurfEasy for VPN and a Samsung S5.