I bought a SparkChart for Literary Terms because I'm taking 2 Lit Exams (American Lit and A/I Lit) coming up and it was $5, plus I had a giftcard, so essentially it cost me nothing.
Other than that, I haven't used any.
I noticed they had one on the Russian Revolution (might be helpful for some of the Rise and Fall of Soviet Union test), as well as Management and Marketing, so it could help for those.
They do a decent job (IMO) of helping you with terms that you can put in a binder and study on lunch breaks/free time, etc. if you do not have access to a computer to use IC, but you can also make paper flashcards to do that, too, for the cost of a pack of cards. It all depends on what you think would help you.

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I'm done!
B.A. English, TESC, completed December 2008

Tests passed: A/I Lit-73, Mgmt-71, Amer Lit-73, Tech Writing-64, Criminal Justice-56, Here's to Your Health-65, Law Enforcement-60