Operational range depends on both ends. If the AP can be heard 10mi away, it doesn't do much good when your laptop/tablet/phone has a low power transmitter that cannot be heard 300ft away. The Nanostation range is _between two nanostations_.
> is communal WiFi users vulnerable to network sniffing?
Yes, however the link is almost always encrypted (WPA-Enterprise, so each link has it's own key.)
> is there something better than Ubiquiti for wide area wifi networks?
That's a shopping question / opinion, and off-topic. (Everybody has their favorite gear.)