My school uses Evolve, but we get both the actual textbooks as well as the online code for the ebooks. This allows you to look up information across the multiple books that you may have. I would not want Ebooks only!!
I hate ebooks to be honest. I took a bunch of gen ed classes that only offered the ebook, and I would always end up printing them out. Personally, I would go with text books, especially for NS classes. You can always keep them on your shelf or sell them to recover some of your cost, which you can't with ebooks. I also like to highlight my texts and I couldn't do that with ebooks. If you could get both (like a friend of mine is), that would be best; you can then use the text for studying and the ebook if you need to refer to it.
Ebooks only is not a good option. Get the regular book if you have a choice. Your computer can malfunction, then you don't have access to the ebook. This happened to me one time and I was without access to my "book" for a very good portion of the semester. Furthermore, the ebook subscription has a time limit, so it is really not a good value. If you want to save money, then rent the text and get one edition old if you can. I rented a one edition old text for $11.99 from chegg.com.
Made on the fly study guides using the evolve ebooks (CTRL+F --> COPY ---> PASTE --> PRINT ... fun times). Loved it to death. The obvious pro for ebooks is they as much as the laptop/netbook you get it from.