Alternative use
I bought a used Brera key fob from ebay. It's attached to a keyring with a prominent Alfa Romeo logo and and left in clear view on a table in my home.
As pointed out, it's expensive and difficult to get these fobs to function as an extra car key.
On the other hand, with opportunistic or targeted burglary (in which the keys are taken to enable the car to be stolen) becoming more prevalent, I think a decoy/dummy key fob on display might be worthwhile given the small expense.
When the thieves get to the car, nothing but disappointment.