From the folders I picked up at the Japan Tourist Agency it appears to be exactly the same Tokyo Metro Open Ticket(s) that can be bought separately elsewhere at NRT. But you are correct in noting it cannot be used on Toei lines as there is a specific note to that effect on the Keisei brochure. There is no such note on the brochure offering just the 1 and 2 day Open Tickets, (Most confusing.)