I didn't use
just IC, and wouldn't recommend doing so either (unless it's a very strong subject for you). IC will give you facts, which is great, but for the test you're required to have a
working knowledge of the information. On the CLEP itself, you'll be asked to interpret data from an experiment, etc. So an understanding of the facts is necessary. I'd highly recommend the following (in addition to IC cards)...
-Go through IC's Biology Feedback if you haven't done so already
-Take Practice Exams (probably the one most important thing in preparation for this test besides the feedback, IMO) REA, Peterson's, and OCSG are all good.
-Go through
This On-Line Biology Book The Collegeboard, the makers of the CLEP, recommend this, and I found it well worth my while. You may also consider looking through what else the Collegeboard recommends for this test:
Study Resources | CLEP
Unless you've recently taken a Biology course or have a working knowledge in it already, then I would
not recommend using just IC's flashcards. This test can be a mile wide and can go deeper then just an inch. This test is by no means an impossible one, but does require adequate preparation. Best of luck!