I switched from the flexfoam-it to kryolan. The kryolan has less issues.
The 2 part polyurethane foams are a lot easier to work with than foam latex, which is, from what I understand, tricky stuff even for professionals. The flexfoam-it is a simple mix by volume, 2:1 ratio. However, in my experience it is affected by temperature, humidity, and mixing time. If any one of those 3 aren't right, the foam will collapse.
The kryolan is better, although all 3 things mentioned above can still ruin your foam. The tolerances are simply greater. It also needs to be measured out precisely by weight, at roughly a 65:35 ratio. Varying the mix will produce softer or stiffer dreads, or go too far either way and you will simply get a sticky gooey mess that you need to clean out of your mold.
The mold needs consideration too...silicone works, but will eventually decay, and is expensive to replace. Ultracal works, but needs sealing and constant release agent application, or the foam will stick to the mold. Seam lines can be tricky with the ultracal molds too.
All in all, there is an excellent reason why not many people do these. It's because they're a pain in the ass, and to make a set for yourself, you will probably spend more than if you were to just buy a set, and in my opinion you don't get any of the satisfaction of say, sculpting a bio or mask. They're just dreads.