Alice, The poly crosses will probably decrease the life of the cut. More than likely it will hack through the gut like a saw. I had VS Gut in my stick and they lasted a while throught he miss hits and everyhting. Gut has alot of power and be be hard to control at times. Adding cut in the cross will aloow you to hit out a tad more without worrying as much about the ball sailing on you. Kepping the gut in the mains will help you maintain more of that gut feel. I believe fed still strings up gut mains poly cross for this fact. So either he feels you will benifit from the set up or he just wants more string jobs. I say give it a shot you may enjoy it.