I usually get 30 ml bottles of things I haven't tried before. Those are my "sample" bottles.
I learned my lesson a long time ago! Don't - Run - Out.
Lately, I've been doing the same thing. When I first starting ordering from FSUSA, I order 10 ml. bottles. So often, I went through the entire bottle within a few days! Now I usually order 30 ml. when I think I'll like it. I hate running out of something I like and having to wait to receive a new order!