You can almost always find a better local deal that works great if you don't move around too much, but Fi is a fantastic "common denominator". Since I've had it I've traveled to...maybe 15 countries in Europe, Central America and Asia and it's worked amazingly well and turned otherwise expensive roaming charges or juggling of sims into normal operations.
It has a weird kind of "global citizen" feel to it that I've never felt any other way. Step off the plane, turn your phone off airplane mode and you're good to go.
Driving across Europe and I received "welcome to " while using Google maps just like driving across the U.S. where it says "welcome to ".
It's also pretty cheap, even if you blow your usage caps and try to go unlimited (Google will cap the charges at some point).
If you stay in one place or travel abroad rarely, I'd say skip it, you can get a local provider with more service cheaper. But if you might end up in an unknown country and just don't want the hassle, it's pretty awesome.