I've ordered from them before but they weren't a "club" at that time. They had good prices at the time I ordered and I think they're even better now if you join. You could compare prices, the price for membership, and whether the membership cost would be less than what you'd pay for supplies at another art supply company (or their retail prices).
I think it would depend on whether you'll be ordering enough to really save. I do see where they are offering a free membership right now and that teacher's can join at half price anyway. You could join right now for free and just see if it's right for you.