Secrets of the Magus provides a number of useful tool for expanding on this new class: arcana, feats, an archetype and magic items. If you need more choices for your Magus, this is a good place to look.
The Secrets of the Magus is a 13-page PDF (9-pages if you remove the cover, OGL page and ads) for the Pathfinder RPG written by Steven D. Russell and published by Rite Publishing.
The layout is primary traditional two columns. The cover is full color while the interior art is color and themed to the magus. It is also fully book marked making it very easy to navigate.
The Secrets of the Magus jumps strait in with new arcana for the Magus, thirty-four of them in fact. Primarily they are offensive abilities but several defensive and utility options are provided as well, some which build upon class ability choices for the Magus. These broaden the arcana options for a Magus considerably.
Another option included for the Magus is the Singer of Blades, designed for elven characters but not restricted to them. It is a class for those who wish to combine the magus with mobility and artistry of the elfin dance. It seems a good archetype and a good addition to the options available to the Magus.
Next are a handful of feats (OK, seven if you want to be precise), all but two of which are tied to Magus abilities. The other two are combat dance feats that tie into the Singer of Blades archetype but could be used by others who have mastered a similar style.
Two magic items and one artefact (Mournsky) keyed to the Magus finish off the product, all of which are interesting but they could be written a bit more clearly.
Disclosure: As a featured reviewer for RPGNow/DriveThroughRPG, I received my copy of this product for free from the publisher for the purpose of this review.
[4 of 5 Stars!]