It works fine
Doug: I have a 310 with Dutchman and the solid Garhauer vang. My topping lift is connected to a continuous circular line that holds the Dutchman control lines. This circular line runs between two blocks - one at the top and one attached to the end of the boom. The solid vang holds the boom up and also tensions the boom during sailing. The topping lift really just provides the degree of tension in the Dutchman control lines. For example, when putting on the sail cover you need a lot of slack in the control lines to get under the sail cover. It's difficult to explain without a diagram or picture, but it works just great. Garhauer makes good stuff.