The size of the user base is still unknown. But one article noted that large number of Binance's traffic came from the U.S. and since regulations have begun to cause problems, that number has dropped bit since then. Obviously this is a significant drop. Now, most of these users probably just bought a VPN to access the crypto trading site. However, it is now easier for U.S. residents to trade.
I haven't used it, but I can definitely say it's the perfect exchange if you're a US resident.