TMO only gives 2G internationally which, while it doesn’t sound terrible, it ends up being unusable in practice. Your experience may vary though I guess.
The last time I tried using it overseas, text-heavy sites like HN loaded almost as fast as normal. Reddit was mostly usable, but certain subreddits were painfully slow due to image-heavy custom styles. But try to load an article from a typical news website, and the connection would time out before it managed to render anything.
I suspect that their partners in europe throttle with an algorithm so aggressive it flat-out breaks TCP.
Remember when web pages were measured in kilobytes? Pepperidge Farms remembers.