The only numbers I've got right now are the 2M+ weekly active users on the chrome web store listing - I've not got exact numbers for how many people use the card readers but I get the impression it's more common in the legacy enterprise/government world.
The 2M+ WAUs would still be vulnerable to the RCE (assuming the native host is setup) independent of whether or not they have a card reader.
The 2M+ WAUs would still be vulnerable to the RCE (assuming the native host is setup) independent of whether or not they have a card reader.