Personally, I've been using this device for several years and have never had any problems inserting or removing the tips. By turning the whole head a quarter turn, you can insert the tips and by turning it a quarter turn the other way, it locks them in place. The mechanism is internal, so there is no visual change.

Hold the handpiece in your left hand. Point away from you. Hold the front part by the ribbing with your right hand and turn it anti-clockwise. When the tool is new, there is relatively great resistance to overcome. The chuck at the tip protrudes by approx. 2 millimetres and opens slightly. This allows the pins of the tools to fit in. Turned in the opposite direction, the tools hold firmly. This is how it works with my device.