I have that the basic syringes where the needle is attached directly to the syringe system easiest to use. You push it in and done. For a couple of years I used an injector where the needle was attached to the hose but I always thought that it was more difficult to insert the needle on the end of a tiny hose, than when attached to a gun.
I do mine when feeding and I lean over the pig and inject on the opposite side to which I am standing. I find that if the pig is going to jerk it's head, then it will not smack into my legs. When you do it, just go for it. The pigs will feel a bit of discomfort for a second, but that's all.
Sbom, as you have got this Panomec now, you could take the opportunity to get your pigs into a regular worming programme. Just twice a year, then you know you are covered for worms, lice etc. Even if you were just intending to use the pigs for meat, at least you know that when you have injected them they will convert the food efficiently. I inject for erysipelas too, as the snorkels are kept outdoors. I am lucky to have a fantastic pig vet nearby and he recommended this approach. Yes, it is an extra expense and hassle but not as much as a sick pig.