The 30 mA earth-leakage sensitivity catches ground faults that could otherwise go unnoticed until someone gets a shock.
The 10 kA Icn at 240 V AC is the rated short-circuit capacity — the maximum fault current the RCBO can safely interrupt. In a domestic or light commercial panel fed by a transformer with a known prospective fault level below 10 kA, this part clears the fault without needing a current-limiting upstream breaker. The 45 A rating at 50 °C means you size it for a continuous load of roughly 36 A (80 % rule for continuous loads per NEC, though local codes vary) — good for a 40 A or 45 A subfeed.
Clip-on DIN rail mounting, 2 modules wide (18 mm per module). Strip length is 14 mm for the top, 13 mm for the bottom. The toggle gives clear ON/OFF indication, and the unit is padlockable with a 4 mm padlock for lockout/tagout.