You have to use there app to access the Wi-Fi? I'd imagine just connecting from your phone and opening IE/Edge would prompt to accept there terms, similar to other places. I can't imagine them allowing Wi-Fi and blocking all connections but their app. That would be a very poor way of doing business IMO. But who knows, I've seen dumber things.
Hmm, just looked at their web site, and if I'm reading it correct, I guess you do have to use their app for their free entertainment... and yes, no windows app, which is kind of crazy in this day and age (350+ million W10 installs (easily more than a few of those are tablets / notebooks))
... If you want Wi-Fi outside of their walled entertainment garden, you have to pay for messaging and/or Wi-Fi.
Always a good idea to load up a phone with offline movies/entertainment prior to take-off.