The only alternative to the Bradt guide is a tiny chapter in Lonely Planet's East Africa guide which doesn't even compare.
The first half of the book goes into the history, (both natural and human) and cultural, travel and other issues that a traveller needs to know. The second half is the guide-book and combines useful information for travellers such as where to eat, sleep and how to get around, with good accuracy. It also has a fantastic feature of articles of interest throughout the book to add colour and detail to every stop.
Prices are now a little out of date, but otherwise great. Get it before hand and read the mine of information it holds.