Air Ducts - Cleaning

Has anyone had their air ducts cleaned professionally? If so, can you give me any info on what to ask, what to look for, what was actually done at your house? I have seen where the duct cleaning company shoves a brush thing into your duct and twirls it around and removes some loose stuff… and I have also seen some type of cleaning where they seal off your ducts and some kind of machine dispenses a solution into the ducts to “sanitize” them. I am juist starting this journey learning about this, so any info would be appreciated. Info on costs also. Thanks.