We won a WiFi Ranger Mobile as a door prize at Escapade last week and it works great. You mount the antenna on the roof, mine is clamped to the top of the ladder, and run the cable inside to a small box that connects to a 12 volt power source.
It finds and boosts WiFi signals and retransmits them like a hotspot. We get a very strong signal in the fiver. It is still susceptible to overloaded campground system slowness, but it does get you a much stronger signal.
I have heard comments like the one above, but have been told that software improvements have corrected the earlier issues.
We only used it for two days on the Elkhart County fairground WiFi, but it worked really well. We're happy with it.
I have used a couple of different antennas in the past and this is the best so far.
A cheaper alternative, which worked pretty well for us was
Bear Extender main drawback is it plugs into a USB port and only works for one device at a time. For a while we each had our own.