I've use a prong collar every day. It is a great tool. I only use a Herm Sprenger, spend a little more money and get a Herm Sprenger. The ones at Petsmart or Petco are garbage. Don't skimp on this collar, saving two dollars will be a huge mistake.
There are too many threads about prong collars lately, most people that bash them simply lack the understanding of how to properly use one and how effect they can be.
Not every dog needs a prong collar, but it is a far safer option than a choke chain or a head halter. If you sent your dog to a trainer then go with what they said and how they instructed you and trained your dog.