In ssh keys all valid ssh keys for the users can be defined. By pressing the plus button additional users and ssh keys can be defined. If one or more ssh key is assigned to a user the previous keys will be overwritten.
Defining (and rotating) ssh keys is a problem that is extensively solved with server automation. In embedded system engineers often overlook the necessity to be able to exchange (or add) ssh keys at a later stage. Either because of security concerns (a device has physically been taken and a key is compromised) or because new services need to be implemented. In many scenarios it makes sense to use different ssh keys for different customer groups. With qbee it is simple to divide installations into customers and use different ssh keys for these different customers.