The Nature Kleen is very good little machine for the money. I do not use it since I am set up with much more powerful oxygen-fed machines, but others have used theirs daily for three years with no problems. IMO they are a far superior unit to anything comarable you can buy from China. I agree the warranties from AquaSun stink, but the units are worthwhile.
As for the 308, I've seen them last for several years and I've seen them cack within several months, so IMO the jury's still out. There are filters and plates which need to be cleaned periodically. This true for ANY corona air purifier. If you do not clean them, the nitric acid destroys them.
I have had good results with the Enaly 200 and 500. It definitely outlasts its warranty and the replacement ozone cells are cheap. They are also easier to clean than the 308. You can find them every day on E-bay.
Hope this helps,