I too at some time in my birding history have been guilty of having used a recording device but I can tell you that there is almost no legal place to use them except your own property. Every Fish and Wildlife service prohibits them, all federal refugees and parks and National Monuments prohibit them and most state parks don't allow them. On our NEK Audubon permit for the State of Vermont I must promise to never use them on field trips.

The other thing one has to think about, when not on public lands is how much interference is 'permissible' for not harming or endangering the birds. I guess everyone has their own scale for that.

Once when I first started birding 15 years ago I just tried a Barred Owl call with my voice in Muir Woods (National Park) and a park ranger read me the riot act. Not only was that embarrassing but taught me a good lesson about something I hadn't thought about. 

I now try to use the recording to play softly to a group I am leading so they can get familiarized with what we are trying to listen for. : )

Tom Berriman