I've been using the Zoom H6 as a field recorder with my camera rig. The EXH-6 allows 2 extra inputs along side the existing inputs on the H6.
The unit plugs into the H6 in the same way as the other add- on capsules.
Connection to the inputs is via non locking combo XLR/TRS sockets, providing both microphone and line inputs with the same specifications as the inputs on the main unit.
Just like the other attachments for the H6, the EXH-6 is a very sturdy, metal cased accessory.
I have seen certain reviws which criticize the use of non-locking XLR sockets. I suppose to a degree the advantage gained by using locking sockets would be a matter of taste. Would you prefer your portable recording device to go flying if a cable is pulled by mistake, or would you prefer it to come out of its socket? In any case, the action of the connection when inserting a plug feels sturdy and secure.
The HXH-6 does not support phantom powered microphones. This, in my view is a major shortcoming, but maybe a 'version 2' will.