The hole pattern of some other spurs doesn't fit for the 4 mounting screws for example. E.g. xray spurs have a 6-hole pattern, not 4 or 8.
Also panaracer spurs are thinner than some others, so the normal button head screws sometimes won't fit those others (flat head screws can possibly be used instead).
Other than these two prerequisites, you're right, it's only pitch and tooth count. All else is just personal preference, quality, price and availability.