The only time I have ever built an flown a model with speedbrakes was about 18 years ago. I had a 100 inch wingspan Osprey glider. I originally built it without speedbrakes and found it very difficult to land. Any time you got near the ground and tried to raise the nose to slow down, it would float for what seemed like an additional 100 yards. I added speedbrakes to the upper surface of the wing just aft of the spar. I put the speedbrake channel on the unused throttle stick. Throttle forward was clean wing, throttle back was speedbrakes full. It became similar to flying a powered plane, with the throttle controlling your decent on approach. Spot landings were then possible.