I continuously circulate when mashing on my direct fired RIMS. I experimented with using a grant a long time ago and I never much cared for it. I did not like having to babysit it full time and I did not want to invest in a lot of level control automation. It was very difficult to maintain a pumping rate that matched the gravity flow from the MT, hence the constant hovering required. I like to pump at a high flow rate in order to turn over the entire liquid volume in the MT as quickly as possible. This greatly reduces the chance of overheating the wort and possible scorching. The fast flow rate also allow me to apply more heat for faster temperature ramp ups when step mashing or for a mash out. The problem is that a high flow rate increases the risk of a stuck mash. My solution, instead of using a grant, was to install a vacuum gauge on the suction side of the pump. I limit the pump suction with the standard flow control valve on the ouput side of the pump. I've learned through experience that anything much above what gravity flow alone would provide is too much. I keep the suction near zero at most 1 or 2 psi. The vacuum gauge provides an early warning of an impending stuck mash. I have two choices when I see the vacuum climbiing. I can stop pumping if I catch it early on and allow the grain bed to relax and loosen up, which it will usually do. I then resume pumping at a slightly slower rate. The other way is to stop pumping, shut off the burner and stir the grain bed, then resume pumping normally. A grant looks like a good idea at first glance, but IMO it's a hassle to use one.