I'm US-based, but just completed a swing through central Europe, packing my Onn stick so I could access US streaming services during downtime.
Like others have reported here, I initially struggled with getting to the hotel's wi-fi authentication screen. I tried everything, including URL manipulation to substitute my (connected) phone's MAC address with the MAC from my Onn. I also tried a bunch of different browsers, even side-loading some (like Firefox Nightly) that aren't in the Play Store for this device.
I finally stumbled on something that worked. . . I loaded Odin browser from the Play Store and pointed it to a nonsensical address, like http://8.8.8.8 -- it never failed to load the sign-in screen, working at two Marriott, two IHG, and three independent hotels.
Let me know if this works for you, or if you have a better solution.