If they can get the latency they're talking about (that Wikipedia page says 7ms, which I assume is round-trip to the satellite), that would be pretty good. If you're on fiber, you should have sub-millisecond latency to the point of presence. Then the question becomes: which is the shorter path, the satellite-to-satellite path or the transit/dark fiber your fiber ISP is using?
I'm not sure how the math works out, but I'd assume for shorter paths (say, your closest AWS region) fiber is going to come out on top, whereas for trans-continental traffic the satellites could be really competitive.
For example, I am getting 6ms total round-trip-time from NYC to AWS in Virginia.