The CAT is running again. However, it is still a tourist trap for the most part.

Unless you need the baggage drop downtown (available for Lufthansa-group operated flights only) on your way to the airport, it is a waste of money. The normal ÖBB trains are much cheaper, only take a few minutes longer, and the same ticket is valid on other public transport in Vienna, whereas the CAT ticket is valid on the CAT only.

Also, keep in mind that the the CAT is only available to/from Wien Mitte. The normal train has a few stops on the way (hence the few minutes longer ride) and additional stops beyond Wien Mitte. One of those stops may be closer to where you want to go/where you come from than Wien Mitte.