How accurate and foolproof are at-home dna tests?

I'm in a little bind here. I might have a son with a married woman. She isn't sure who the father is and I want to be discreet about our situation. I've seen the at home dna testing kits and I am curious about whether they will be as accurate as a test done at a testing facility. I don't want to sacrifice quality for convenience, I want to be 100% sure on this. Any feedback would be greatly appreciated.