Are they as good as banks claims or are they full of it?
Full of **it. But it seems opinions vary along 6.0 or 7.3 lines.
If you have a 7.3, save your money. Get a MBRP 4" exhaust, an AFE, Tymar or AIS intake, gauges and mounting of your choice of style and mounting. Top it off with chip or programmer from DP-Tuner, Wildman, Beans or other reputable place.
Banks is overated and overpriced. I made that mistake several years ago and it cost me significantly to do it all over the right way.
If you examine Banks own test numbers, you will see that the numbers they claim are not at the max torque or HP point. If they claim a gain of 90 - 100 hp, it will be at some point well before or after the peak points. So in fact you might only see a maximum gain of say 50 hp at peak, when you are expecting a gain of 90 - 100 hp.