In my case it was complete product failure vs consumer error, although that was the angle SSBC was trying to push.
They went on just fine, although yes I do agree the rear kit instructions are very vague.

I had problems with the crossover tubes on the front calipers leaking. Tightened some more, leaking. Tightened more, still leaking. Finally sent them back to SSBC, to which they replied they were going to repair them vs replace them. I thought they were nuts, but they refused to replace them. I got them back & on the car, they still leaked but this time I got them to stop. They then BLEW APART while bleeding the brakes. I sent them back yet again where they found they were assembled with the incorrect tensile strength bolts from manufacturing. Scary stuff indeed. At this point SSBC refused to offer me a refund because the brakes had been installed (still zero miles on the car mind you).

I found the rear caliper mounting brackets to be on the flimsy side, they have quite a bit of flex to them.
Stu, whatever you do, take Dayclona's advice & do NOT use the wheel studs they give you! With a mere 23 miles on the car the rear wheel studs FAILED. I lost one lug, and almost completely lost a wheel. I don't know what tensile strength steel they are made of, but upon inspection I found the knurls on all the wheel studs rounded off, the studs were flattened smooth. And yes, I know how to install wheel studs, and yes the wheels were torqued properly. There were plenty of threads for the lugs to engage as well.

A friend of mine just had front hubs fail on his SSBC kit on his Dart, they were on the car for about 8 years or so. He nearly lost a wheel, and resulted in quite a bit of damage to his car.

These are just my experiences. I know several people that use & like them just fine. But based on my experiences I won't use their products on my cars ever again.