IMHO, it should never be used on double coated breeds. It can and does strip the undercoat- something you particularly do not want in breeds like Labrador Retrievers who need that undercoat. I'm sure you've seen the commercials/infomercials where someone is using the furminator/shedender and it is tugging on the coat. The reason why it is tugging is because it is getting all the undercoat, not just the dead loose stuff like they'd like you to believe. Think about it, it would have no reason to tug like that if it wasn't pulling out all the undercoat.
I personally use and recommend the Zoom Groom as a safer alternative. It gently removes any loose, dead hairs as well as any dust, dirt, or debris that might have settled into or on the coat.
Just my 2c,
Darcy
