What this breaker is
It's designed for IEC 60947-2 industrial applications — mechanical engineering and industry panels — not domestic distribution boards.
The quick assembly system clips onto the rail without tools. IP20 is achieved only with connected conductors.
Thermal derating — the real-world rating
The 4 A rating holds at 35 °C ambient. At 40 °C it's 3.71 A; at 45 °C, 3.55 A; at 50 °C, 3.4 A; at 55 °C, 3.22 A. Humidity also plays: max 95% up to 55 °C, dropping to 35% at 75 °C. The breaker itself is rated for -40 to 75 °C operating ambient, but the load current you can pass shrinks as the panel heats up.