TD Books Reader is designed to provide an open access eBook reader for those with ePub and other format eBooks on their iPhones or in their Dropbox folder, but it lacks the functionality and performance to do it well. While there is certainly room for an independent eBook reader app on the App Store, TD Books Reader fails to stand out as anything more than an early iteration of what have become very smooth, easy-to-use apps.
The result of this is that the navigation, setup, and use of any one book in TD Books Reader is needlessly frustrating. Changing text size, adjusting the screen resolution and brightness, and leaving bookmarks are all harder than necessary thanks to a cramped menu and multiple submenus that hide important functions. By default the text is impossibly small to read so you'll almost certainly need to change things, which you'll have to do every time you read a new book as it resets with each new book you read. While Dropbox integration is very welcome--something other eBook readers should seriously consider adding--the interface once you load an eBook is sorely lacking. Fortunately, performance is never an issue. Pages turn quickly and the bookmarks load fast, so if you don't mind the menu issues, the app will work for your needs.
In the end, TD Books Reader is an acceptable replacement if you prefer not to use a corporate eBook reader from Apple, Amazon, or Barnes & Noble (among others). The downside is that it's not as good as those corporate options, and for those who want simplicity, it will present more frustration than reward, at least at first.