The problem with Wazine is that it only gets rid of round worms, chickens pick up a lot more the just round worms. So if your going to spend money on a wormer and time worming you are just as well off to use something effective. Valbazen will kill everything a chicken can pick up. Chickens are going to get worms, not if but when, there's just no two ways about it.
As far as waiting until chickens are so infested that they look bad and have worms and worm eggs in their poop? I'm sorry but I find that very poor advice. By that time they have a very heavy load of parasites and a lot of internal damage. Why let them get in that state before doing something about it? And yes, you can do fecals but you have to do them a lot because if the parasites are not shedding eggs at the time you do the fecal you will get a false negative. Far better off for the health of the birds to be on a regular and rotating deworming schedule.