Mixed
I took my friend flying in my Chief, and after about 10 hrs I let him fly from takeoff to landing on straight skis and a 3 mile long lake for is birthday. He was hooked, and went out and bought his own Chief, at which time I sat him down with both of our families and said "no solo until a flight instructor signs you off". We had flown a lot together, and I never really worried about who had the brakes because we almost never used them.
The flight instructor had the same misgivings, (pilot only brakes) and while flying off pavement, had two "swap ends",(almost ground loops?). The second one they were so "against" each other on the rudder pedals that it bent parts on the torque tube. He had just about had it with flight instructors until he just happened to meet one at work. Went flying with him and that guy ended up signing him off. The lesson both he and I know is that your not done FLYING until its stopped and tied down. Flying an airplane with what I call "pretend" cable actuated mechanical brakes has made both of us better at staying ahead of the airplane. Furthermore, especially on skis, when your heading for the ditch, what seems like the wrong thing, is really the right thing. THROTTLE OUT and FLY THE TAIL.
If its his airplane and he wants to risk it, give him the brakes, pick your flying days, and go get yourself into a little taxi trouble with it, slowly and on purpose. Find some grass gravel or ice. Help giude him in finding out what can happen, he probably will anyway. I know I did. Or put in brakes.