The late great Sheldon Brown had this to say about Brooks (and other suspended leather) saddles:
Plastic saddles have four advantages over leather ones:
- They are lighter.
- They are weatherproof.
- They do not require breaking in.
- They are cheaper.
Leather saddles have three advantages over plastic:
- The big advantage: they are much more comfortable!
- They are generally more durable;
- They can be repaired.
He has more to say here:
https://www.sheldonbrown.com/leather.html