I have been using the Sibley eGuide for about 4 months and I enjoy it very much. The content is outstanding, since it includes all of the birds of North America including rarities. This actually makes it a very good value when you compare the cost of the app to a comprehensive field guide in book form. Variations for each species are shown. There are usually several different recorded bird calls for each species - this is one of my favorite features of this app. I also like the "compare" feature, where you can pull up any two species side-by-side. For someone who is somewhat new to birding and bird identification, this app has been an outstanding help.
If you are serious about keeping lists, you might not be satisfied with this app. I like that I can see "My List" of birds, overall, by date, or by location, and can email my list as a .csv file. But there is room for improvement. It would be great if the lists could be compatible with eBird, the Cornell citizen-science data collection project. I also wish that some of the links in My Birds were more interactive....e.g. I wish I could click on a species in my list and have it take me to the overview page for that bird. I also wish there were a "checkmark" at the top of each overview page where I could see at a glance that I have seen that species, where and when. In the notes for this app I see that there are plans in the future to introduce new features in this area, which I look forward to.
Overall, great app, highly recommended for anyone who loves birds and wants to learn more about them.
MinnesotaBirder about The Sibley eGuide, v1.8