BookReader is one of the better e-book readers available for the Mac. There is a lot to like, especially control of line spacing. For those who are merely reading, this is a good environment. Not being able to read DRM-crippled e-books in third party software should bother no one; Apples iBooks (coming with OS X 10.9) has a monopoly on that capability.
However, the interface makes no provision for the user who is using e-books for reference while writing or communicating with others. The user must somehow work around the unchangeable twin page layout. Even with a large display, I find that difficult enough that I have made do with less sophisticated e-readers that at least have an option for single page display, so as to have room for the windows of several other applications.
Additionally, I find it helpful, especially when making text selections, to have a scrolling mode available. This eliminates frequently having to highlight or copy part of a text, flip the page, then select and highlight or copy again. Thirdly, I prefer to have the option of ragged right with no hyphenation, which I believe makes for better eye movement and reading comprehension, not to mention aesthetics.