I have used the graco many times and really like the airless sprayers. Yeah the motor only runs when there is a pressure drop. The biggest downfall of them to me is the clean up. Have to run enough thinner through them to clean the whole line. I believe they come with 25 ft. So it's a little product that you use up. It's not a big deal if you are going to be using them frequently, can just use the thinner to thin down your next batch to spray. A nice feature is that if you have a lot of spraying to do just shove the suction tube in a gallon or five gallon pail and have at it.
I am leaning towards buying a graco as my next sprayer. Probably for the money and times I use it a year the x5 or x7