The answer to “what is the reasonable number of free-action attacks” is simply zero, because one should not get free-action attacks. Throwing Shield should never have been printed saying that you could.
Pathfinder has a standard way of having things give “extra” attacks, and that is through “bonus attacks.” And there are several things about bonus attacks that are worth bearing in mind here:
Bonus attacks represent attacking faster somehow. You are able to simply move faster than someone else (e.g. haste), or you are able to make simultaneous attacks (swinging a weapon with each arm at the same time, say).
Bonus attacks are good. They are considered valuable class features. People go out of their way to get them. That isn’t to say that every bonus attack on offer is worth it—levels and feats are very valuable after all—but it’s not because bonus attacks aren’t good that people quibble over the costs.
Bonus attacks are starkly limited. You get one from most sources that offer them. Getting more tends to require more investment—more levels, more feats, and so on. Some sources even block you from getting more from certain other sources—consider the haste spell and a speed weapon, for example.
Bonus attacks come at a cost. A −2 penalty on all your attacks for the turn is a common one (e.g. flurry of blows, two-weapon fighting), but a spell slot is another possibility (e.g. haste), and there could be other options. A speed weapon doesn’t have a cost to use beyond being a speed weapon, but as a +3 property it’s very pricey.
Bonus attacks can only be used in a full-attack. That means a full-round action, making it very difficult to move into position if you aren’t already, and it also makes bonus attacks incompatible with various other options, e.g. Manyshot or Vital Strike.
If you have any ability to attack as a free action, the last bullet point doesn’t come into play. That means we expect the feature to have very significant limits, and/or considerable cost to use, or maybe, be available only at very high level (and still have some limits and/or cost to use).
The throwing shield is available at low level for little gold, costs nothing to use, and offers no limitations. As such, it should never, ever be offering free-action attacks. And in fact, nothing about the throwing shield makes it any faster to attack with than any other weapon you might have in your hand—so it shouldn’t even be offering a regular bonus attack either. Nothing about the description of the throwing shield suggests it should be faster than another weapon—just faster than another shield that you would have to unstrap.
And on this, Paizo’s FAQ agrees... sort of.
Throwing Shield: The throwing shield says that it has special straps “that allow you to unclasp and throw it as a free action.” It seems likely that “unclasp and throw” means “unclasp in order to throw” but it could also mean “unclasp and additionally throw” which could give a character any number of extra attacks. Which interpretation is correct?
Throwing shield’s wording means you can unclasp as a free action in order to throw it; throwing it would requires its own action. The wording will be updated to disambiguate in the next errata.
I say “sort of,” because Paizo attempts to worm their way out of responsibility for the error, by claiming that the text “could” mean that you get free-action attacks, and so the proposed errata would “disambiguate” things. This is an inaccurate description of the situation. The text not only “could” mean that, it quite simply does mean that—there is no version of the English language where “throw it as a free action” means “in order to throw it as a free action.” That’s not how the language works, and it is disingenuous of Paizo to claim that it does. There is no possible ambiguity here. So make no mistake, the text describing the throwing shield is simply an error. The proposed errata would be a correction, not a disambiguation. Unfortunately, this is a behavior that Paizo engages in often, and it is to the detriment of their audience because it makes us all a little less clear on what the rules are, and that the words they use mean what they say. Mistakes happen, it’s understandable and unavoidable, but they have to be clearly recognized, admitted, and corrected. This kind of weaseling out of that just makes things harder for us to play the game.
In this case, I offer that explanation of the situation because I want it to be exceptionally clear to the reader that you are not reading this incorrectly. Rather, instead, this is a situation where Paizo has written it incorrectly.
- Since no errata has been released since this FAQ in March 2017, the “next errata” mentioned here does not actually exist, and given that it’s been three years and there is a second edition of Pathfinder now, it probably never will.