Finally got the chance to use Portal outside the house during Christmas.
Tried at at both my parent's house and my parents in law.
Have to say, despite them having basic internet bundles, it works almost as good as at home, i.e. almost like playing on my tv (minus 4K/HDR/120hz).
Tried MW3, Fortnite, FF XIV and Pinball FX and they all ran completely fine.
No idea why some people have so many issues with performance on Portal. It must really be their internet connections that are causing issues, but that's an ISP/internet issue, outside of Portal.
Spend pretty much all my gametime on Portal and today I booted up Horizon on my tv and I agree that it's a shame Portal doesn't have an OLED screen and HDR, but for me personally, the convenience of Portal makes up for the lack of OLED/HDR.
(In particular being able to play games whenever I want while chilling on the couch with my fam, or when me and my gf are being lazy in bed during the weekends).