I have three of them and I have only used one when taking a class. It was helpful when I wanted to practice what I was learning. But I find that if I want to do a practice run before putting it on a cake I just do it on a plate.
I keep them because I have kids who want to learn and they will be useful for them. (People gave them to me, I didn't buy three!) Before I wound up with three of them I had planned to put the practice sheets in a page protector and just use that (clear plastic).
The value for you will depend on whether you use it or not. 
If you get interested in doing gum paste or fondant you can use the practice board for several things, also. It's good to roll out small pieces (lift the clear piece to peel them off after they're cut) or to store the cut pieces to prevent them from drying out while you're working.
For practicing icing, that can be done on a practice board, plate, wax paper, whatever. It depends on what you are going to do.
My practice board came in a kit--otherwise I don't think I'd actually buy one. It's an ok reference, but if you have icing techniques shown elsewhere (book, etc) I agree with deena1987...just do your practice on wax paper.
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