I have 3c hair I use the argan oil one and it works fin3 for me. As far as amt, section hair into sections and apply a little bit at a time till you get your desireed look. That's how I know how much to use on my hair
I am wondering about Ecostylers as well because I just discovered that I can get them pretty easily here in the Netherlands for only €3,95 per 16 oz tub. I've done a lot of research already but it seems that it elongates curls (my wavy wurly hair does absolutely not need that) and that it is particularly 3s and 4s that like it.
F - LP - HD - NE
Fine, low porosity, high density, normal elasticity
Low poo: Petal Fresh Organics Rosemary & Mint Volumizing Shampoo Protein: Colorful Neutral Protein Filler Detangler/RO: KCKT (winter) or Curl Junkie Beauticurls Argan & Olive Oil (summer) Styling: KCCC