Potential job starts on casual contract?

So I found a job advertised online, advertised and a full time permanent position.

I applied, got an interview and was pretty much offered the job as they were showing me around.

However they said they would start me on a casual contract to begin with, and in a months time review my performance and move me to a full time contract if all is well.

Is this a normal thing or should I be concerned about this?

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