Hum, meta-data items should be displayed for all objects whatever their type (at least in the most recent version).
I'm more concerned about your getClassID method: you should actually return either the CUSTOM_H_OBJECT ID or the CUSTOM_LEAF_OBJECT ID (depending on whether you want to allow the item to have children or not). The ccCustomHObject already return CUSTOM_H_OBJECT by default.
Own properties in plugin
Re: Own properties in plugin
Daniel, CloudCompare admin