I've installed the unit on our coleman Mach III ducted AC unit. Quiet enough to easily carry on a conversation in the trailer, quiet enough to not annoy us. Much quieter than stock. Don't mind having the AC on anymore.
The only downside is that it eliminates the ability to bypass the ducts and vent directly. If the trailer is hot, it was nice to bypass the ducting and get the cold air into the main living area.
For us it was well worth the cost. Yes, it is pretty spendy but it is well designed and easy to install.