The yellow triangle on the ASI has a specific meaning. It's the recommended approach speed at maximum gross weight in calm conditions. A skilled pilot should be able to make a well executed full airbrake approach / flare / touchdown starting at this approach speed. The roundout will be brief. Adding a little speed (5 kts) gives a little more time in the transition from steep approach to landing for learning purposes.

With most airbrakes, the reduction in lift (at constant speed, AoA) happens in the first 2" of deployment, while the effect on drag is fairly linear over the whole range. The pilot must coordinate pitch attitude appropriately with airbrake deployment to control airspeed. If the airbrakes are opened just slightly and held there, a little back stick pressure may be required. If opened more fully, some forward stick is almost always required. That's a general characteristic of gliders with Schempp Hirth airbrakes.

The 2007 accident sounds like one of Piggot's sub gravity sensation accidents.