I recently got some pure carrageenan to see if I could recreate Genutine with other gums. My best effort produced marshmallow fluff. It seems locust bean gum is essential. Locust bean gum is also very difficult to find and expensive too. L'Epicerie carries it.
Bottom line, get the Genutine. Save some money. Save the hassle. Make marshmallows with Genutine.
No, I'm not on their payroll. :-)