This question is something no one can really answer besides you.
Only you can estimate your current level in both verbal and quant. You should ask yourself the following questions:
1. Whats my current level
2. How much time i have to "waste" on GMAT
3. Can I really do it by myself or am I clueless?
4. Do I have the money and time for a full course?
5. How important it is for you?
Bottom line - the only reason not to take a course is either you dont want to waste money or you do not have enough time. So - you should decide whether you can and want to invest both.
I believe that a course can only help...
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