The roofer is doing you a disservice if he's installing 2 rows on the roof at the eaves. They aren't made to catch sliding snow and ice. It won't happen.
Here's a link showing the proper installation techniques. http://www.albertsroofing.com/SnowGu...stallation.htm
I wouldn't even give a contract to install two rows, or even three. I'd pass.
To better understand how it works, have somebody roll a bowling ball down a sliding board for you to catch with your stationary hand at the bottom.
Then, in the middle of the sliding board, have somebody place the bowling ball against your hand.
BTW, I charge $16.00 to maybe even $40. per guard to install, depending on the roof, accessibility, etc.