That photo shows the lock in its storage pouch, it opens out to a 6 sided lock around the frame so check with your insurers first to see if it complies.This looks good, we have 2 Bromptons but our insurance said we must have a heavy D lock and must be secured through the triangle of the frame as shown in your photo. (Anywhere else and the bike can be folded/taken apart to remove the lock).
Our locks are Abus Bordo 6000/75's, there are other versions like the 6000/90 which has longer sides which afaik won't fit the frame in the stored position.
https://www.abus.com/uk/Mobile-Security/Bike-Safety-and-Security/Locks/Folding-locks/Bordo-6000
Pete