Multiple usage tickets have a very special behaviour. It manages limits for each device separately.
If you give a 1h ticket with multiple usage, it will be one hour per device, no matter the number of devices.
I will think more about a "multi usage" option in the access class.
The problems I see with simultaneous usage are:
If you have a 1giga or 1hour limit ticket.
You use this ticket on 2 devices. If you use everything (1giga) in one session, both devices will get 1 giga.
If both devices consume half a giga and then disconnect, you won't be able to connect anymore, because both devices used 1 giga.