The only thing you might miss is the ability to get certain advanced jobs when you hit 30 for the first time, but for you to manage to get that far in only 30 days you'd have to stop functioning in the outside world for most of the trial. It's easier to level these days, but still.

Jobs to 18, subjob quest, jobs to 30, advanced job.

I personally think SE is retarded to only have a 30 day trial for a such a hardcore game. If they'd make it 60 days they'd probably hook a lot more people. But if you just want a bit of the flavor, you're not gonna miss too much.