Great Mask !!
Your friend should be happy : It is the M30 mask with "Mikro Anschluss" : A mike could be added for communication.
These were used a lot by Kriegsmarine and also by Heer... It looks like yours is a Heer model: can't see any Eagle with M stamp on the inside of your mask.
Does the mask have the same name as the cannister ??
I also love the "Merkblatt"
Here a few pictures of the M30 with mike
MP44.nl - Welcome to my Website
Very nice! It's in great shape, too. Now you need to get some extra lens' to go in the compartment under the lid they aren't too pricey, if you decide to get a couple.
The stamps are great and I also like the instruction paper.