I will start by saying that the strategy of 123 magic is actually a really good one. However, It was hard to get through the author's demeaning writing. He constantly refers to children as "annoying" and reminds you that by using the strategy, you will get kids "to do what you want" and you'll "be able to enjoy them again" as if they're little dolls meant to serve you.
He also tells you throughout the book to make sure you don' argue back (great advice), show no emotion when kids are acting up (super solid advice), and don't ever explain yourself or let your kids tell you how they feel or why (not great advice). I agree that explaining yourself or trying to talk reason into the kids is not appropriate during a tantrum, but it is important to listen to your kids and have heartfelt conversations later (he specifically tells you not to do this later), and make sure that your kids feel heard while also understanding boundaries and why they're there.
His advice about locking children in a room for timeout while they kick and scream makes me want to call the police on him. He even notes that this is illegal in some places. God forbid there was a fire... He relies heavily on timeouts (which many studies have proved just make kids better liars and more resentful), but he does offer many examples of "timeout alternatives" which is what I use if my kids get to a three.
As I said, though, this actually is a great strategy of counting (why it's not a 1 star review), and used with reasonableness and compassion, it definitely works. I read the novel "How to Talk so Your Kids Will Listen" (which should be called "How to Listen so Your Kids Will Talk" because that's really what it's about), and with those parenting strategies and the the 123 method, you could have boundaries and compassion.