I am an international student so take what I will say with a grain of salt. I'm studying for the GRE (have been studying for a couple of months, not systematically but generally going through the trouble of looking up words I don't know). I gave freerice a try and I was moving around levels 40-44. Having said that, the words that appear in freerice I think are far weirder than what you encounter in GRE. Off the top of my head: "telamon". I study classics so I figured it out, but I'm pretty sure that at least 90% of the people who live in the English speaking world do not know what it means and in fact have never heard/read it, and it's highly unlikely that you'll find that in a GRE exercise. Same goes with words like "menhir", or "taiga". They can't ask you what the opposite of "taiga" is. Worst case scenario: taiga will come up in a text about forests, but when they're in a text more often than not you can figure words out even if you don't know what exactly they mean.
I scored 660 in a Barrons GRE verbal test I took. Not dissapointed, but I'd like to score a 700+.
Also, "chanterelle". What the hell is that about. I cook, so I know what it is, but words like that don't constitute the familiarity with a language, but more like your general and encyclopedic knowledge.
My advice: Use freerice for fun, GRE tests for properly studying.