Best economy add on = a vacuum gauge. Driving the car with a light and steady foot will keep the gauge in the 18"-10" of vacuum range that produces the best fuel economy. Get down below 10" of vacuum and you are getting into the area that sucks up gas.
Well say what you want about the headers and fan. I was there for the dyno pull b4 and after at my local racing shop and saw the car go from 187 peak hp to 207 hp with panel filter and headers. The first engine i ran the black tragic on was my 302 with TF twisted's, Cobra intake, E cam, and all of the other bolt ons and It worked perfectly for the 6 years I had it. I'm just talking from my personal experience, not what I've heard from others.
I was going on the assumption that most people are running a taurus, spal, ect... Black magic does come up every now and then but even according to the manual it is only rated for 240hp w/ac or 300hp without I believe so yes. I do praise the ease of install on the black magic but for most people it just won't cut it for their engines. True some people get lucky and get an above average fan so more power to them... whatever works i say... I was able to run my fan setup on the stock alt. for a little while so it will work but at some long stop lights I was watching my volts go down to 11.5 at idle.
Kevin