Their main selling point is the longevity of the coating which, in normal use, can be between 18 months - 4 years depending on the coating used (generally the more expensive coatings contain a higher percentage of the active resin compound). There are several brands of ceramic coatings currently available on the market and not all are equal - Gyeon, GTechniq, CQuartz to name a few.
The car needs to be carefully prepped to make a ceramic coating last anywhere near as long as stated by the manufacturer, for me, that is reason enough to avoid dealer applied coatings altogether. They simply don't have the time or expertise to decontaminate the car properly, polish the paintwork to a high standard and then apply multiple layers of ceramic coating to each surface (wheels, paintwork, glass etc.).
Applying these coatings without doing the prep will significantly reduce their lifetime and will also seal in any swirl marks, buffer trails or imperfections in the paint - which you will find present on any brand new vehicle. If you're considering it at all, you should go to a reputable car detailer. Although potentially more expensive, their prices will reflect the time spent preparing the vehicle to take the coating.
Personally, I think the return on investment from these coatings depends on the vehicle's usage and the cleaning/maintenance routine.
It's important to note that ceramic coating paintwork is not a one-off exercise, the hydrophobic properties tend to wear off pretty quickly so it still needs to be topped up with a "top coat" every 3-6 months to maintain the water repelling characteristics. The base protection layers in these coatings are particularly susceptible to water-spotting issues and, without the top coat, can end up making the car look worse, even if the paint underneath is safe.
Ceramic coating glass generally requires a high level of preparation and can cause all kinds of ghosting and wiper judder issues if not done right.
Ceramic coating wheels is usually always a good investment as it makes cleaning them much easier and helps prevent at least some of the red-hot brake dust from sticking to the clear coat on the wheels.
Improper wash techniques and harsh cleaning chemicals (found at most car washes) will also accelerate the deterioration of the coatings and reduce your ROI.
You may also want to look into paint protection film (PPF) if you really want to protect the paintwork from things like stone chips, light scratches etc. Ceramic coatings aren't magic and don't really offer any protection beyond what a high quality wax would give you, they just last significantly longer.
