I have been ripped off by "professional" leafleting companies more than once.
Hiring your own distributors gets monotonous as after 1000-2000 the youth that reply to the ads get fed up, so they either do not deliver them, or put 4/5 in each door to finish quicker, just happen to pick all streets with terraced houses so they get them out quicker, even if you specify where they should go.
If you are going to supervise them personally, then you may as well deliver them yourself,because you will fold them the correct way, you will deliver them solus, they will actually get in the door.
You may not get so many out, but you will get a true response rate if you do them yourself.