I have been using extensively Merlin since a couple of years, perhaps three, specially after a large pack of European species was added to the list of species supported, boosting its performance in my area. I wish I would have had such a wonderful aid for learning bird sounds on spot when I started birding long ago, so I am very grateful to Cornell! My hearing is far from good, and many times it alerts me about the presence of a particular species allowing me to detect it visually, or by hearing if they get closer/louder. As with every tool, common sense in using the app is important. I do not pretend, for example, to rely on a tentative ID given on the pair Common/Spotless starling here in winter, or to get every single "chirp" IDed correctly. In some situations I can "hear" and ID some species directly from reading the sonogram even if Merlin is not ID-ing them (i.e. firecrest). In other cases, playing the recording close to my ears confirms the species I haven't been able to hear "live". Understanding how it works is also important to know its strenghts and limitations. Short calls are difficult, mimicry difficults correct ID, while in a chorus with several species the app usually is in advantage. For what it is worth, I use it in a daily basis at Spain with the "Spain" package installed on Ebird and always using positioning (tracking) in my device, and cannot recall to have have been suggested an American species (after the mentioned improvement, before I got them), although sometimes makes obvious false calls. It also still lacks some important species here (it is useful to have a look at the supported species list from time to time). But in the whole is fairly consistent. I would never expect a 100% success (as I don't also with many guides, etc...) Of course, each one has its own opinion and birding circumstances, abilities and limitations. The above ones are my shoes...