This is a good starting product for those wishing to have their magus dip its toes in the waters of other classes. Admittedly I was afraid that this product was just going to be nothing but "X levels of magus counts as levels in (insert class name here) for ability Y" but was pleasantly surprised to find they put some thought into this. Most of the abilities herein offer either thematic boosts to concentration checks when used with other class abilities or allows the magus to spend arcane points for things like rounds of bloodrage/rage (or vice versa but in a creative and balanced fashion).
The only thing from holding this back for a full 5 star review is that I feel that more could be done here to expand the intended function of these feats, since they are a band-aid for the problem of multiclassing. things like the barbarian/bloodrager one allowing specifically the casting of spells for spell combat would have been appreciated to offset the cost of multiclassing more.
To sum up
I enjoyed this product and found it balanced and functional, but I feel the multiclass gap could have further mitigated with these feats. For a step below perfection I give this a 4.5 star review rounded up to 5.

So my first review that I spent all night on got eaten. So instead of my option by option notes ill instead do the highlights
1st the bad (aka the only reason this isn't 5 stars and my new favorite thing ever)
the reprint of the gunslinger loses amateur gunslinger for a new deed, which they cannot use without grit. This continues with the swashbuckler on both regular and dedicated options.
Monks were not improved enough on either of their options to take.
lots of copy paste errors throughout.
Eldritch knight seems to increase you spellcasting altogether by up to 2 levels, including getting early access to next level spells.

The amazing
Reasonable handling of prestige classes that makes me consider taking them with only feats on the line.
honestly the other options the were missed out in unchained are pretty good.
Dedicated Multiclassing is a tough pill to swallow for the sacrifice, but most of the options at least present a case to be tempting to those that can afford to give up all but their 1st feat.

Despite the score I'm giving I do think this book is worth getting as the useful options present a powerful character making tool for players and gms alike.

While I doubt I could add much to the awesome review that catmanbeck did, which addressed many of my same concerns, I feel the need to say my piece about this class. First off this class gives a very Shadowmancer/Fearomancer impression, so if that concept excites you this is well worth the buy. Heck I already have 2 players fighting over who can play one in my next campaign, and I will gladly allow it. I'd describe it's fucntion in relation to other classes thusly, take the Sandman Bard, add in a dash of witch and magus, and just a smattering of cthulhu(with the right build and archetype anyway) and it ends up a solid debuff class with good anti mage and combat capabilities. Their Dire zone downright seals the deal on a battlefield control role, Especially when combined with eldritch tendrils (see cthulhu comment).

The archetypes presented are even more exciting when they narrow down the various concepts of the direlock.
Banelock: The Combat loving aspects of the Direlock brought out more.
Dreadmasque: In my personal opinion this made the purchase worth it alone. The fact their mask has multiple forms, with a distinct feel and associated witches hex, is what makes this a wonderful and well thought out archetype.
Fear Eater:...YOU EAT FREAKIN FEAR!!! this IS the Fearomancer, hands down, and if you wanted to make a memorable villain this will definitely do the trick. I personally am going to design a cthulhu-esq Aboleth with levels in this, a BBEG my players won't be forgetting anytime soon.

All in all, a good start to Forest Guardian Press. While not perfect, it is seriously one of my favorite downloaded classes thus far. I will be looking forward to future products from this up and comer.