The Pro S2 features the highest quality of metal work, electronics, and motors along with the most up to date and responsive 6 axis gyrometer anti-collision of all our Chinese manufactured desk frames. The Pro S2 has also tested best in range for stability. The European S4 is of a similarly high-quality standard and shares many of the same features as the Pro S2 but is based around a Linak® mechanism and Kick and Click® frame. This product has been manufactured wholly in Europe with the benefit of many years of engineering experience and refinement that comes with the Linak® brand.
For a full analysis see this page https://www.gostand.co.uk/pages/desk-comparison-v3