The Trapper gains very useful abilities while losing access to spells that he wouldn't have access to anyways for many levels to come. Essentially [unless you don't want to deprive the party rogue of disarming magical traps] if you're dipping in ranger for less than 4 levels there's no reason not to dip in trapper (as well). I haven't seen any other situation where that is the case. For example, while the falconer gets a (very limited) companion right away, he gives up wild empathy for that, an ability available at first ranger level. Or for skirmisher a late ability gets replaced with a different late ability. Do you think this was intended, or am I missing something and the trapper archetype is only available at 4th level?
Further, the Guide's Ranger Focus (Ex) seemed balanced, because it allows him as a swift action to apply the equivalent of a favored enemy bonus to a target in line of sigh of any race – however only once per day (until higher levels). Freebooter is similar to Guide in that it replaces favored enemy and hunter's bond; but the Freebooter's +1 bonus to attack and damage rolls (applied as a move action until target is dead or new target is picked) doesn't have any kind of daily limit, and applies not only to the Freebooter, but all his allies within 30 ft as well. At higher levels the Guide get's additional uses and the bonus gets larger, so it balances out – but at low levels the Freebooter seems quite a lot more powerful.
Say a rogue(knife-master&scout) wants to dip in ranger(trapper&freebooter), is that a legitimate combination?
The Knife master gave up magical trap disarming for extra sneak damage when using knives and the trapper gives that back, while allowing use of better knives (kukri) and armor (mithral shirt+armored kilt), Freebooter's Bane (Ex), track, wild empathy, some more class skills, slightly better bab/hit die. It seems very powerful, but is there anything mechanically wrong with it?