Is it obvious to onlookers that you're doing something to the target?
You use the power of suggestion and subtle psychic influence to alter a subject's mind and dredge up repressed memories.
(Emphasis mine)
You are simply talking to the target, whereas the target becomes more sluggish as he enters a trance. Someone standing right next to your target might notice the difference, but from a distance it would only seem as if you're having a conversation.
Does the target remember the command?
If he remembered the command, then wouldn't he automatically become unwilling since he knows there was someone ordering him? The clause about a target ceasing to be willing indicates that they leave their trance-like state after the suggestion has been implanted.
Does an unwilling target get the Will saves?
An unwilling target would simply not listen to you. So he doesn't need to make the saves, since he wouldn't let you use your ability.
*****Anyway, the Diplomacy skill can already do what this ability describes.
You can use Bluff and Diplomacy together to make a request of a creature, without it even realizing you have made the request.
Check: You can gradually coax a target into thinking a suggestion is entirely its own idea, making the creature more likely to act on the idea than if you had suggested it outright. You discuss topics subtly relevant to the request, asking leading questions and narrowing the scope of the conversation so that the target eventually decides to take a specific action you have led it to.
You first attempt a Bluff check to convince the target that your request was actually its idea. This is always treated as far-fetched circumstances, resulting in a –10 penalty on the check. If successful, you then attempt a Diplomacy check to make the request of the creature, treating its attitude toward you as indifferent for this single request (regardless of its actual attitude).
Action: Planting a notion and then coaxing a target into suggesting the notion himself each require at least 1 minute of continuous interaction. This can be difficult to arrange with a hostile or unfriendly creature.
And this one can actually be used on hostile and unfriendly creatures.
*****
The hypnotism would work better against targets with high sense motive/charisma, so in those cases it would be useful.
But if I didn't have access to occult skill unlocks from a class, I wouldn't waste a feat to get hypnotism.
This is from the Magic section of the core rule book.
Some spells restrict you to willing targets only. Declaring yourself as a willing target is something that can be done at any time (even if you're flat-footed or it isn't your turn). Unconscious creatures are automatically considered willing, but a character who is conscious but immobile or helpless (such as one who is bound, cowering, grappling, paralyzed, pinned, or stunned) is not automatically willing.
Not sure if that would only apply to Spells and SLAs but it may apply here as well.
Since you implant "as suggestion" I would assume unconscious targets are considered willing per the magic section of the CRB.