Disclaimer: I received a free copy of this product for the purpose of this review.
This is a full-color, 86-page product. As the name suggests, Horses and Mules focuses on things relating to steeds and their use. The product opens with a section detailing the biology of horses, with occasional notes on how donkeys and mules are different. Normally, I don't actually think too highly of these sections - but I felt this part of the book actually came in useful, since some of the things it addressed might be relevant to players using steeds in creative ways. For example, the inability to see certain colors, or their drastically improved hearing, might actually come into play every now and then. Towards the end of this section, the various terms are all broken down into game mechanics - for example, moving at a trot would be considered hustling, while a gallop is the equivalent of running.
Starting on Page 20, we get statistics for different kinds of horses, from large warhorses to small, dog-sized breeds. There's also a table for horse personalities, helping to give added flavor to a creature whose activities are often just hand-waved by a group.
Page 35 is where we start to get into the real material of this book, and it opens up with a section on horse-related skills. These are mostly copied from the CRB, but there are a few new options inserted. I'm not actually sure how to feel about this - on the one hand, I dislike too much copying of CRB content. On the other hand, having all of this could be helpful if someone wanted to print out the section for use at a game table (although they could also print the CRB's stuff, when you think about it). Having additional options helps, but it's difficult for me to call this part either good or bad.
The section on feats is similar, acting as a mix of new and old brought together in one place for easy reference. This is quite helpful for those who don't want to search every book they own for related feats, but also serves to pad out the content. I mean, don't get me wrong, there's new material here - but not quite as much as you might expect if you look at the page count. This continues until around the time we get to the Hussar, a new full-BAB base class focused on the use of mounts. In that regard, it's fairly similar to the cavalier, and includes a few archetypes for added specialization.
After this class, we get a little more magic, including some notes on how to obtain magical steeds, a list of horse-like creatures by CR, and statblocks for quite a few of them. As before, though, a lot of this is collecting information from different sources into one place.
In the end, I think that's what stops me from giving full marks to this product. Don't get me wrong - having a lot of rules for one concept brought together and expanded on in one product is not a bad thing. In fact, it can be very useful. However, I really would like to see a little more original content in this line. To me, this product is a solid 4/5 - it certainly accomplishes its goal, and I have no major complaints about it, but it doesn't go quite far enough with offering new content to earn full marks.
[4 of 5 Stars!]