I guess you can't really expect it to be a smooth ride, but I'd recommend only going one way and then possibly walking back to get a different perspective on scenery from St. Aubin to St. Helier. Alternatively public transit (which is 4x less the price) runs late so there is always that option if you choose to eat dinner in St. Aubin.
The audio wasn't that audible because of the traffic noise all around, but the facts that were audible were interesting, making note of Elizabeth Castle and First Tower. If you have young children I'm sure they would be thrilled with the novelty of riding in a train, but otherwise I would recommend saving that pocket change for something more worthwhile.
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