I use a Verizon 4510 MiFi at our campground and when we travel. Like now, sitting in a Florida resort. Free WiFi is dragged down by the available bandwidth divided by the number of users on it, including kids playing internet games or watching videos. If my MiFi slows down the "free" WiFi, I really don't care. Where did the information come from that a personal MiFi will slow down a public WiFi if it's in the same area?
2.4 WiFi has channels 1-11. Think of WiFi it as 15 lane highway. Your signal is like a very wide vehicle that is 5 lanes wide with the center of the vehicle in the channel # lane. You can think of the vehicle as a half circle where most of the weight (signal) is in the center lane and and least in the farthest out lanes.
If everyone in a RV park including the camp ground would use channels 1, 6, 11 it would minimize the interference. All three can go down the highway side by side and not even touch. However most people don't even know how to set the channel on their wifi. Many things like MiFi do auto channel selection and unfortunately their channel selection choice is often not very good.
If you have a smart phone you can download a WiFi analyzer app which will display on your phone what signals are around you so you can set to a channel that will minimize the interference.
channel 1: -1 + 0 + 1 + 2 + 3 ( note -1 and 0 can not be selected - so the WiFi won't intefere outside the band it is allowed to use)
channel 6: 4 + 5 + 6 + 7 +8
channel 11: 9 + 10 + 11 + 12 + 13 ( note 12 and 13 can not be selected - so the WiFi won't interfere outside the band )
When two people with WiFi try to use exactly the same channel then the interference is worst. The farther apart the channels are the better.
The signal on a MiFi will only go about 25 yards in terms of its ability to cause interference. Cradlepoint is high power and can interfere with neighbors 100 yards away, in particular if its channel is set exactly the same as the campgrounds.
To be good neighbors use a wifi analyzer app and set your hot spot 5 channels away from the strongest campground channel and to maximize your own results use a channel that does not have a strong signal from a nearby space.