I paid considerably more than $2 for my PDF copy of the Tome of Secrets, because I bought it early on, before the errata......and hardly anything changed with the errata when I downloaded that errata'd version on RPGNow.
The book isn't too bad, but it's still kinda disappointing and incomplete.
The races are okay but don't have much detail, nor do the classes have much descriptive text. The races might be a bit better or worse than those in the PF core, but not by much. Would've liked to see at least a sidebar of favored class listings or 3.5 conversion stats for the races, just for a bit more utility. Considering the book's name, Tome of Secrets, I would've expected some material of a more flavorful and neat or unusual sort (time magic, strange races, tricky feats and spells, dark and mysterious magic items, magical tech, or at least more fantasy firearm-related stuff; but nope, little if any of that kinda stuff in the book).
The Artificer is either gimped or overpowered, depending on how the DM interprets its strange rules mechanics and terribly vague Wierd Science device details. A good class if those vagaries and potentially-broken parts were filled-in or houseruled. But unuseable in its raw, printed form.
The Knight is rather limited and I'm not sure if it's quite on-par with a PF Fighter overall......it's not necessarily bad, just very narrowly focused and not any better for it.
The Priest is basically a cloistered cleric but might be a bit underpowered for what it gives up in raw fighting ability (at least, relative to a PF Cleric). Not sure.
The Shaman is similar to a Cleric or Priest, but with a narrower focus on spirits and a sort of limited yet diverse possible spell selection......I think it's weaker than a PF Cleric, but it's hard to judge without seeing one in play or something.
The Spellblade is a disappointingly barebones and underpowered take on a fighter/mage hybrid. It's playable, but a bit weaker than a PF Bard. Its signature class feature could also use a bit of clarification on the limits of how much total effective enhancement bonus equivalent they can grant to their weapons when applying special abilities (like Flaming) alongside enhancement bonuses.
The Swashbuckler is a solid fighter/rogue hybrid, though its table has one or two minor errors (missing the Weapon Mastery entry at 5th-level or whatever, and I think something else might've been off a bit?) and it's unclear if they're supposed to get any further Weapon Mastery beyond that point or if they're supposed to have access to Fighter-specific feats or not (despite having stuff like Weapon Specialization in their bonus feat list, it seems that they still need to take several levels in the Fighter class beforehand in order to qualify for those feats). Would've liked to see one or two more skills on their class list, such as Knowledge (Nobility). The Swashbuckler is, however, kind of disappointingly limited in scope; only really effective with piercing weapons and light armor, no special options or the like for different techniques or heroic acts of derring-do, and nothing to make use of Intelligence or Charisma beyond the standard skill modifiers. Nonetheless, a solid class anyway.
The Warlock is a brokenly weak or brokenly strong endless-caster, like the ones from 3.5...... They need more clarification on how wizard school abilities function for them and how often they can use them (since many wizard school abilities have a use limit, whereas many warlock-specific school abilities do not, and they're supposed to be able to use school abilities at-will). Their DR is a bit messed up and possibly abuseable (though minor, so it doesn't matter too much). They're too weak unless they take certain school abilities, which then make them overly powerful unless the DM clarifies or fixes those ones to function more reasonably than the vague descriptions imply. Also, they have practically no need for Charisma or any other particular ability score.
The Warlord seems reasonably solid like the Swashbuckler, but also has a few minor vagaries in its details. Nothing major that I can recall. Might be somewhat too strong in some cases, considering the temporary HP it can grant the group multiple times per day, but I'm not sure; it might just be on-par with a PF Paladin or somewhat weaker overall.
I haven't read as much of the other material in the book, but I remember wishing there was a bit more firearms-related stuff and wishing that some of the firearms stuff they had in there was a little more balanced/useful.
As far as other 3rd-party publishers go........ I've bought a handful of SuperGenius Games' PDFs off the Paizo website, but have been on the fence about them since reading them. The classes tend to be a bit overpowered and a bit too narrowly-focused in some cases, and the naming of a few class features etc. is pretty bad (due to trying to emulate some names from D&D without directly copying them). Haven't found any DM yet who'll allow me to play any non-core Pathfinder classes or the like, anyway, besides Paizo's own Advanced Player's Guide. And that book's just plain broken in some parts, especially with the Summoner.