I totally agree. I think it's unkind to sneak them into the coop after dark and hope for the best. I liken it to waking up standing in someone else's bedroom for the new chickens and for the existing flock, waking up to find a stranger sitting in your bed next to you. Slow and steady wins the race.I have my resident flock and I have a recently acquired mini flock (which held 4, 1 died, leaves 3).
Last weekend, I was given two more hens (who had been vaccinated). My logic was, the 3 from the mini flock had been with me one month (quarantine time!). The 2 new one's were vaccinated (not sure the 3 mini flock had been) and I took the risk of integrating the 2 new, with the 3 mini's. I would NOT have done this with my resident flock - I chose them specifically; these last additions were given as part of a package for the housing the seller was selling.
Intro's on the first day were, as expected, very henny! The pecking order was on full throttle, to say the least! Today? The odd nip but nothing worthy of note. So, within 3 days, all is settling down nicely.
Now, come the warmer weather, I will need to amalgamate my resident flock with the mini-flock. This will be done via free-ranging expeditions and familiarisation. It could take weeks, may even take a couple of months - I'm ok with that because I will have more time then than I have now.
Both approaches do work; but the safest approach is the gradual approach as opposed to the bung-em-in-at-the-deep-end one.