We love ours and find it much quieter than any rooftop unit - even higher end coaches.
Just last week we were in Amarillo at 104F with no shade and it kept us very comfy in the 70's. Over 11 years it has always been adequate even for very long stretches of hot weather.
As others have posted, downside is availability of parts, service, and repairs.
Ours works perfectly well on 30 amp service. It starts one compressor at a time and settles out at about 22 amps. If we use the microwave, electric water, etc., the EMS will shut off one compressor while the other appliance is working. So, we prefer 50 amps, but 30 works just fine and has kept the coach very cool in extreme heat. Just have to be careful about using other electric draws.