It cheaper to buy a stick and the 18gb than top up and it has a 365 day expiry on it.
There's nothing particularly onerous in the exclusions and small print.
Mobile Broadband: Prepaid Mobile Broadband: Prepaid devices are locked to the Crazy John's network. A $100 fee applies if network locking is removed within the first 6 months from activation date. Recharge before credit expires and accumulate unused data, maximum NEW balance after recharge is 20GB. Included data only for use in Australia on Vodafone's network. Broadband speeds are available in Vodafone's 3G Mobile Broadband Zone. Slower speeds can be expected outside Vodafone's 3G Mobile Broadband Zone.