I am running an unopened 95 Cobra with a Vortech v3 @14lbs of boost at redline. NGK TR6IX plugs at 0.034 and at first the car was good all the way to redline with just an MSD blaster coil. Coil failed shortly, car broke up at 4500 with stock coil. Went to screamin demon coil and the car pulled to redline without spark blowout for a few days and then above 5300 it was back. Finally installed a MSD 6AL and absolutely no spark blowout. I know people knock them, but so far mine has solved my issue. Reliability will be the next question.
Do most need one, nope. The stock tfi systems pretty damn capable for most combos. I wouldn't bother with one on any "real street car" still running on your typical 91-93 octane pump gas. Now a track toy or something built to rev it can be beneficial but a typical basic ignition box on a mild build is absolutely pointless if it doesn't have a timing control or a rev limiter. Spark wise its not going to make more power.
Stock Fox Ignition System = Good!
Stock Fox Electrical System = Teh Suxxorz
My setup includes a Kenne Bell. Everything in the ignition system is stock except for my Boost-A-Spark. What it does is keep the coil saturated and regulated at an adjustable setting up to around 19V and is wired directly to the battery. Other electrical system demands don't affect coil saturation... This stays constant at your preset.