Metal gets fatigue ... if it is strained over it's limit.
As long as you keep it within it's limits ... depending on the exact alloy ... it's going to be fine and will make for an excellent suspension.
The rubber bit makes sure the metal can't move further than it's supposed to go.
Personally I can see a huge future for this sort of suspension.
When done right it can really help and it doesn't add any weight to the bike.