Obviously it isn't, but also obviously: this isn't a web browser in anything but technical implementation. It's a packaged, sold, interface to a proprietary service with a set of T&Cs that they are free to enforce.

Also every single one of these that I've seen before has fallen down in the same way. Chat apps that embed Facebook, third party YouTube viewer for Apple's VR headset, various other third party Instagram apps, etc.

Even if it is legal, meta and google will just block you from accessing the service.