Its awsum product I buyed two years before and in my family there are two symphony cooler aslo are a cheaper option than air conditioner.
They work well in dry areas, in humid climates they are not effective and hence can be avoided.Direct evaporative coolers are the most common, used to lower the temperature of air by using latent heat of evaporation, changing water to vapor.
Two stage cooling goes through 2 stages. In the first stage the air is precooled by heat exchanger.The precooled air in second stage through water soaked pads. Since precooled air goes through in the second stage, in this type of cooler the humidity will be less.
Air coolers use less energy than an AC. Air coolers need less maintenance than an AC. Also does not need elaborate installation and hence this cost is almost negligeble unless you have some special requirements.