It does not rust, unlike stainless steel, which eventually degrades.
For me, the biggest drawback is stability. In the case of a ladder, unless it is firmly attached at close intervals, it tends to become wobbly the higher it extends. Cheaper products also have a tendency to become brittle and break.
On the other hand, composites are usually durable and easy to clean and don't tend to develop much lime scale.
In the case of stainless steel, if it's good quality, then there are no major drawbacks. I have not seen any severely degraded equipment, provided it was appropriate quality to begin with. You do have to watch out for the choice of alloy in the welding in case the equipment is exposed to chlorine or ozone, which can be very hard on metal.
Both composite and stainless steel work well, depending on your budget and your particular installation.
My preference is for composite because of its longevity. However, if you are using the equipment outdoors and it is exposed to a lot of sun, you are best off with stainless steel.