I'm one of the 'new parts' guys. However, let's look at what I would look to buy new anyway:
Power Slot Rotors - 209.99
Hawk Pads - 114.99
Braided lines - 84.99
Total - 409.97
Difference of $540.02. That's serious premium to pay for spindles, figuring you can find the right setup with everything for ~$200.
Now me, personally, have actually had an easier time finding just spindle hub assemblies. So all that extra hardware (caliper bolts at 7$ a pop from Ford) and still having to source Cobra calipers, the $540.02 price tag plummets, probably closer to the $200-300 range. But that still leaves you out sourcing used parts that you have no inkling to the history of. Worth it? Possibly. But, I'd replace all the hardware anyway (Banjo bolts, caliper bolts, hubs [or at the very least hub bearings], and dust shields if the spindles don't have them.
An added bonus is the kit leaves you with an easier time cleaning everything before you give them a a fresh coat.
It absolutely comes with a premium, something you can easily circumvent yourself as 5L is proof of. However, for me, as I plan on replacing the shocks/arms/k member anyway, I'd probably shoot for this kit over anything.
In sum, to each his own, but this kit isn't that horribly priced overall.