[whipsaw]

It appears to me that there are a lot of traders, although I don't know for sure. One way I measure that is the quality of the lines, and at least for baseball they're always top notch (often the best line in the market on both sides, and usually no more than 3-4 cents apart--sometimes even one cent apart). Even football lines are often less than 5 cents apart, which tells me that there is tons of competition out there between wagerers.

The only thing I don't like about Matchbook is that they don't offer a ton of props, and the long term futures are not heavily bet. But for standard betting of moneylines, spreads, and totals, it's everything a basic bettor needs.