You can use another Radius based authentication service like Purple Wifi to get a similar functionality.
It's free up to 5 Access Points and offers bandwidth limiting (speed/time/data), pre-generated vouchers and Pay-to-use (through PayPal).
It also allows you to customise the Captive Web Portal.
According to the support team they'll hopefully be exposing the vouchers to their API so you can, in theory, create vouchers on your POS or other systems and issue them to your customers.
