Sciguyjim,
I use both products. For what it costs, and the way I use it, I think Nufinish is a very good product. It keeps my truck shiny and makes it very easy to wash. This is important to me as it takes forever to wash a full-size truck. The truck sits outside in the full Sacramento sun all year long. After 5 years of use, the paint I haven't scratched (its a 4X4) still looks and feels good.
I use the Blackfire on my daily driver. It is garaged when home, but it sits in the sun while I'm at work. I've only put 2 coats of the blackfire on. The blackfire seems to be lasting just fine, its been on over 2 months now, and the cars paint still seems to have a "glow" to it. It is a different look than the Nufinish and it does not make the paint feel "slick", but I like the way it makes my white paint look a alot.