The Gevers telescopic wing actually has fewer critical moving parts than a complex fowler flap does. A component failure is less likely to occur in the telescopic wing and if it does, components are redundant and the design is also fail-safe. Redundancy means that a single component failure such as an extension cable breaking does not affect the actuation of the wing. Fail-safe means that if multiple components fail the wings will simply stop in the current position. If this occurs, the aircraft can still fly, land, and maneuver with the wings in any position.
Asymmetric extension is prevented by the design more so than with some conventional flaps.
So the Gevers telescopic design is simple and safe. Weight and drag are the obstacles to achieving high performance. The wing drag is the sum of two components, induced drag and parasite drag. Induced drag is due to lift and parasite drag is mainly due to surface friction. Increasing the size of a wing increases its parasite drag.