There are other wormers available, injectable and oral (via a crop feed), should you need to treat some birds but not others or want to be certain on each getting the correct dose. But like you said, there may not be a need for worming if regular worm counts indicate there isn’t a worm burden.
Have you seen any evidence of blackhead in the chickens so far? That strangely bright yellow pooh? I used to have a flock that carried it (separate from our turkeys), google cayenne pepper as treatment, I’m not guaranteeing it works as I only used it twice which is not exactly enough to qualify as sound scientific research
but I was under the impression both times that it worked, it didn’t seem like coincidence.One thing to keep in mind is the amount of pooh turkeys produce - an awful lot more than chickens!
Larger birds - more feed - more pooh! The more space you can give them, the better.
As for despatch, a sock over the head is useful. Over their head, that is, not yours!
Oh, and turkey poults are the sweetest ever, we hatched them ourselves so maybe that makes a difference but they were all super friendly.
Good luck!