I don't have the Milwaukee bagger fender extension or their line of bags, but I do have something very similar. I purchased my bags from Eastern Performance. They are the abs injected mold type. They needed the usual prep before paint. Seem very durable so far and my fender extension which is similar in fitment but not so in shape and is trimmable I got from a company called motorcyclepaint.com at a very low price considering the alternative. I do know that I won't be keeping the fender extension for long because I want to go with a whole fender replacement in the future, but for the price it was perfect. Until I fund my other items on my wishlist, this full fender replacement for me will be last thing.
I don't have one, but one of the main reasons I went with Top Shops fender cover is because a couple of people I know have had problems with the durabilty of the MB street sweeper. It looks and fits good, but due to the issues, I decided on another option, price is about the same. And I got to keep the rear lower light.
2010 FLTRX With Plenty of extras, goes by the name "Hardeshia"