I have sold a number of upgrades and 100% of the people said that they love it, not just like it, love it. Really quiets them down quite a bit. As far as the dry side replacements go, they are $199 to replace the dry side. So if you do the math, $75 for the driver, $75 for the wet side and $199 for the dry side then you get the price of a new Mp40 QD which is $349. So you can build one yourself for the same price.
We try and stock the wet sides and replacement drivers all the time along with the whole new MP40QD pumps but don't have the dry sides in stock and probably never will.
Hope that helps!
Cris