Cool, so that sensor will let you use Zwift on the iPad but you won't get the full effect of resistance changing on the hills and when drafting etc - you will need a smart turbo for that. They start at about £200 and you can spend £1k on one if you really want.
I haven't used Zwift with a "normal" turbo before, but Zwift have created zPower "power profiles" for some common non-smart trainers, these will be more accurate than other turbos. You can find a list of the turbos that Zwift have created these profiles for here:
http://zwift.com/hardware#ready
To be honest, I don't know how or where you tell the app that you are using one of those turbos (assuming that you are, perhaps yours isn't on that list) but if you are using a turbo that is on the list then you should have a better experience if the app knows you are using one of those turbos specifically.