I have not used any chemicals and also have never noticed any smell.
I do use a Camco Dual Flush every trip to fill the tank a couple times & dump every trip. I am always surprised at how much "stuff" still comes out of the tank after flushing 2 & 3 times.
I would never just dump my tank (even when full) and assume everything will make its way out... wont happen. I have seen it with my own eyes that you need lots of water. Whether its by bucket, hose, back flusher or tank cleaner it is the only way to make a tank clean and odorless.
Deodorizing chemicals probably work, but if you just spend a little time to do it correct, you shouldn't even need them. At least that is my .02.