Interesting - it appears that for iOS and Microsoft clients, the information is not in the DHCP options but part of the 802.11 beacon. See Best "metered connection" settings for public mobile hotspot? (in public transport setting) - RUTX12 - Teltonika Networks - Teltonika Community
I agree it would be nice if Peplink had a button “mark as metered connection” that would automatically handle all 3 options for us.