I've used the collars on my dogs for years and will continue to use them. I live in a Lyme disease hot zone, and it seems like every year ticks are more prolific (now is the worst time of the year). Moreover, my neighbor recently came down with Rocky Mountain spotted fever. No way am I letting the dogs out of the house without some protection.
I consider Seresto to be the best type I can use. One of the benefits is that if there is a reaction, the collar is easily removed. You can't do that with topicals or ingested products like Advantus.
I was just talking about this story today with friends at my local dog-training club. We have our own grapevine, people who train and breed, and none of us have heard of any of the problems reported here. There are pesticides involved, so yeah, you want to be careful -- wash hands after exposure -- and alert to behavioral changes in the pet.
Tick tick tick tock goes the clock on the wall as we're dancing the evening away -- Tick Tock Polka