It won't automatically redeem them for you if that's what you're worried about. It will tell you how many points= voucher. Even if you do redeem them by accident, what you get is a coupon code that you can either use immediately or wait to use. I don't think they expire and I don't remember there being an increased return if you collect a huge amount of points. You get what you get in evenly spaced increments.
OR:
http://www.madvapes.com/redeem.asp
40 points is $2.00, 100 points is $5.00 150 points is $7.50 from that you should be able to figure out any amount.