I bought a set of Eaton Detroit rear springs and that is what is on the car now, happy with them, but for the price I paid I should be happy. From what I have been able to gather the main issue with the less expensive springs is that they make a few sets of them for what are a ton of different applications. What this will impact the most if your ride height. Your car could end up too high or too low. With the Eaton Springs, they make them specifically for each individual application, they all are a little different to make sure that the ride and your ride height is what Ford intended. I know that there are some people that have had bad luck with some of the off brand leaf springs coming from overseas, but in reality they seem to be few and far between. The front coil spring seems to be much more critical, there are a ton of people with issues with the overseas front springs, mostly because their cars sit way too high. I bought some Moog front springs, I think the part number was 8356, and the car is about an inch too high in the front. If I were to do it again I would buy the Eaton Detroit springs for the front. From what I can see for front springs definitely get the Eaton ones, and for the rears you can probably get some of the less expensive stuff.
Here is the deal, if you want it to be perfect, or at least the way Ford intended, Eaton Detroit is probably the only way you will get that. If you are willing to have some difference in ride height and ride, then the off shore stuff will work. Most of the time there are workarounds to get your ride height where you want it to be if the springs you buy will not get you what you want.