I've been curious about this class for a while, and finally decided to drop the $3.00 to see it for myself.
Gotta say, I'm pretty impressed. This is at the very least nearly on par with Paizo's own base classes, and is a very well thought-out tinkerer/artificer type class -- kind of a rarity.
Machinesmiths do Crafting, Prototyping (IE spellcasting), and Combat, and they have a series of tricks that support each of these subgroups, as well as a Greatwork item -- basically a super-special-awesome signature gadget that continually upgrades and becomes more powerful. In this text they cover Mobius Weapons (an enhanced/bonded weapon option), Analyzers (multipurpose sensing/divining instrument), and Mechanuses (eidolon-like pets). Between each of these plus the usual feat allotment, the Mechanicus offers a lot of versatility within a well-focused concept. If you favor control, you could take a Mechanus and some crossbow turrets and camp out behind the front lines; if you favor up-close and personal, take the Bull's Strength prototype and a melee Mobius Weapon -- you're on the d8 hit die/+15 attack progression, so with all the enhancements it's very reasonable. It's an easy class to build around, as well, as the only real requisite for anything is a solid Intelligence score.
In the end, though, the Machinesmith always comes back to being a SUPPORT character above all else -- whether as a support fighter, a support caster, a support archer, a pet summoner, et cetera. You can rest assured that you'll be reliable in whatever it is you do, but you won't necessarily overpower other classes. It's more akin to a Bard in many ways than to other spellcasters. Unlike the Bard, who accomplishes support through performance, though, your party maintenance comes in the form of outfitting the group with superior gear, sending out drones, using Prototypes and leveraging whatever flexibility your Greatwork grants in order to adapt to your situation.
And adaptability is absolutely the name of the game. As a few examples:
-Prototypes work most closely to wizard spells, with Machinesmiths preparing them out of a book of Blueprints as needed, and they can be prepared a good deal quicker than wizard spells of equivalent level.
-Mobius Weapons offer the ability to switch a set of feats on and off, turning you into exactly the kind of support fighter you need to be to suit the situation at hand.
-Machinesmith Tricks can either augment your Greatwork, provide passive bonuses, or give you new gadgets; alternatively, Combat Trick is always an option.
-Machinesmiths get all the major knowledge skills; coupled with an Analyzer, they can be masters of information.
All in all, I dig the heck out of this class. I think it's very well-designed, and as balanced as anything Paizo themselves has made. It fills the same role as a Bard, and offers a more "hands-on" approach to support with a few more options than passively switching performance off and on -- however, it doesn't displace a Bard's role or importance in a party, in that it doesn't have as many skills and isn't quite as reliable for buffs; the key being that nothing Machinesmith does adds morale bonuses. Meanwhile it won't displace a Wizard either; if anything, it benefits greatly from having other casters around to collaborate with, particularly with Collaborative Crafting.
That said, the PDF could use some work on the formatting and flow of information, and the Machinesmith Tricks list is a bit scant. Manageable, which is the upside, but scant. It would be nice if the text for how Prototypes work were moved to the section with the spell list and new spells instead of at the top of the PDF, for instance. Meanwhile, while the artwork is generally very good, sometimes the images aren't in exactly the most relevant places -- a picture of a Mechanus is on the page for Mobius Weapons, for example, and every so often there's just a random image with no relation to the current text, seemingly just to make the composition of the page more attractive. Certainly can't fault that, you work with what art you've got, and to their credit LPJ got good art. Other than that, it's very consistent with Paizo's own standard of printing.
This one gets a hearty recommendation, and I'll be picking up the expansion PDF, "Cutting Edge Machinesmith," as I'm dying to have more content. I sort of wish LPJ would take the two and collect it in one more clearly sectioned volume, though, so as to not have to jump between two PDFs.
[4 of 5 Stars!]