To comply with the ABYC Standard, the longest distance, measured along the conductor between the
shore power inlet and the first OCPD is 10'.
In the case of a combo ELCI and CB such as the Blue Sea product, the assembly can be installed close to the inlet in a watertight box, left on, with the control taking place at the panelboard as usual. No need to open the lazerette unless the ELCI or CB trips.
The unit you provided a link for is an ELCI only so it does not provide the OCP that ABYC specifies.