The 36 mm width takes up 2 modular width units, so it fits in a standard 18 mm/module panel grid. Mounting position is any, so vertical or horizontal rail orientation works.
The 72 V DC maximum is the highest voltage this breaker can safely interrupt in a DC circuit. If your DC bus is 48 V or 60 V, this breaker covers it. The C-curve (5–10x In) avoids tripping on the startup surge of a small DC motor or a bank of capacitors — a B-curve would nuisance-trip on the same load. For DC circuits, that's a solid margin for most panelboard faults.
Halogen-free and silicon-free construction — important for clean rooms or environments where outgassing could contaminate optics or electronics. The sealable cover (yes) lets a panel builder or inspector lock the toggle position after commissioning.