I also use Gun Free Zone on my phone. But it seems locally (Denver) that they've populated it with a bunch of locations but no information. E.g. they list a bunch of doctor's offices as 'gun unfriendly' but they're all in an insurance company's office building, and there are NO comments from citizens either way about these offices. I had to enter my own apartment complex in there because it was listed no information.
So it's a good concept, but not populated enough by gun owners as to 'friendly' or 'enemy'. At least they were wise enough to know there is no middle ground.