When I wrote the previous post I hadn't activated the SIM I only did this yesterday.
Imagine my surprise to discover that the $19 price included 5Gb of data for a month. This data from Telstra normally costs $30 a month (I did tell you they were expensive) but was part of the package.
For a moment I was worried that it might be a pre paid contract but I double checked and it isn't. Well that's the data for my holiday next week sorted.
With this in mind it might be worth looking out for a similar deal on these dongles perhaps they are trying to just get rid of them. In this case the free data is less than two thirds the price even if I throw away the dongle when the data expires next month.