When you realease Metal and Amex support outside the UK there are two main selling points if you want people to get it and use the card. That doesn’t include insurance. Most (all?) of us who would consider another premium card already got them with the high level expensive Amex cards. Keep it simple!
Higher limits is a must for Metal.
A new cashback program. What about something like the Revolut metal but better than 1% outside, 0,1% inside the union? Stimulates use and referrals for growth. Maybe 1% all over with a maximum of £15/month just like the fee or slightly higher at a sustainable level. That way people get awarded with a free Metal as long as they keep spending. They get more points for free from the underlying cards and are really happy with that. Of course this all depends on your businessgoal. Just my quick thoughts.
Edit. Make the Metal «nordic» for us. Not common but still some merchants here in Scandinavia just accept cards with nordic code. The first six numbers of the card I belive.