Downside 1: it does not stop rocks
A coating is a few microns of hardened silica. It blocks UV, stops etching and makes the surface slick. A stone at highway speed goes straight through it to the paint. If chips are your problem, that is paint protection film, not a coating. Most cars we do get both: film on the front, coating over everything.
Downside 2: it locks in what is under it
A coating is clear and permanent for years. Swirls, water spots and holograms under it are sealed in until the coating is polished off. That is why every coating we apply goes on paint that has been decontaminated and machine-corrected under inspection lights first. A coating over uncorrected paint is the most common bad job we see from other shops and from dealerships.
Downside 3: it is not self-cleaning
Dirt sticks less and rinses off more easily. It still has to be rinsed. Bird droppings and love bugs should still come off within a day. Automatic brush washes still abrade it.
Downside 4: it costs more than it looks like it should
Ceramic Pro packages start at $499. Most of that is labor: wash, iron and tar removal, clay, correction, panel wipe, application, cure in a controlled bay. The bottle is the cheap part. A coating priced like a wax is a wax.
What is not a downside
Washing is easier, gloss is deeper, and with the right package the warranty runs from 2 years to lifetime.
