Their typical sale is buy 3, get one free. Of course when they do that, the price of the tires is like $185 each. When they don't have the sale, the price on the tires is like $155 each. Total marketing ploy to make you think you are getting much more for your money.
Anyways, I've never liked ProComp tires. Their design has been constantly rated low in tests by the various off-road magazines. People here on the board complain about the tires wearing out fast. On the flip side, I've seen people praise the tires. Seems there really isn't a clear concensus about any brand of tires. Me personally, I dislike BFG tires and love my Goodyear MT/Rs. They are pricey as hell, but are a really good tire, IMHO.
So anyways...do whatever you want. My opinion usually means nothing.