However, doing it without training, without an association with an actual law enforcement agency, and without transparent operational guidelines that the public can inspect at any time strikes me as a bad idea at best and vigilantism at worst.

Absolutely. This was my first question on reading their site...who are these nutters and why aren't they telling us about themselves in any open and honest way. Not expecting them to tell us where they operate from but at least giving casual readers enough to find out whether they're legit.

And for me, "think of the children" does not, of itself, make them legit.