I am thinking about buying some used flic buttons. I've however noticed that the first batch is not firmware upgradable and thus not what I want to be buying.
What can I ask from the seller to identify that these are not from the first batch? Maybe color is already enough? It's a 6pack with 3 black, a teal, a creme and a green button.

Are there any other hardware tweaks in the newer models that I should be aware of?