My friend and I actually had that problem with the cheap flaring tools. We had some coated brake lines (from an Autozone or O'Reilly) we used and for whatever reason the flaring tool couldn't get a good grip onto it to flare it so we had to borrow one of my friend's tools to get the job done. But later on we decided to swap over to the non-coated lines as that also improved flaring and bending capabilities.

So NAPA should have a "quality" kind. I'd like to get a start on this tomorrow so maybe I'll drive on down in the morning.