Unless you are trying to conceal a kid or yourself if you can't get in the brush they are a waste of time, money, and are not as effective as backing in to a bush.
They are excellent where you'll be stationary for long periods of time, want some protection from the elements, want some extra concealment to flop around with a bow and arrow, or you are taking the young ones out. Not your typical coyote calling scenario.
They might have some merit if you have the patience and determination to stake out a carcase or something where the added warmth and long term concealment would be a bonus.
I hunted out of one during deer season with a first time hunter this year with excellent results. I have also used one in the last couple of late gun deer seasons when the weather was bad - single digit temps, wind, snow, etc...
Add a propane heater and some good coffee and you're set.
For the typical 15-30 minute coyote calling stand they are not a good idea. Just like Billy The Kid said.