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Not me, but I'd imagine it would be pretty easy like cleaning that composite decking I see everywhere. It scratches pretty easy and permanently, but withstands basic cleaning procedures and most chemicals.

I also helped a local builder on a stack of composite shingles that was sitting on a job site a bit too long for the liking and they became dark and spotty. Obviously growing mold he was very concerned for his buyer and his name. These I believe they were calling E-Shakes they had a formal name I think it was Enviro or Environ shake. Anyway there was a holdoff with the job and they say in the shade for a good while getting damp for months and he called us up to take a look and we cleaned them with a H2O2 solution I use that is about 22% then we spread them out in the sun. They seemed to really hold in the moisture and dried out a bit when in the sunlight not to mention the growth dissapated. I think the sun was the real pro on this one.
The real knowledge I gained here is these things are crap.
From a products standpoint and its biological growth capabilities I believe you have to consider the electrical charge of the product if you are dealing with a polomer. A magnet sprayer would be best if you get the right chemical to breaK its bond. But the grooved textured plastic cedar may be of the hardest thing to clean.

Yeah the ESA (Environmental Solutions Agency) called me up and we had top clean those decks because they gave a "no mold" guarantee. And that, ofcourse, help up like pant without a belt. They agreed to clean the decks as opposed to replacing them. (I assume this is the same suit)
We tried doing there protocol and it was just stupid. We had to hand scrub these things for hours and it still left them spotty. Then we got smart and threw their products in the trash along with the $225 per deck we were getting for cleaning decks when we were not allowed to use anything stronger than a hose. But ofcourse they let you use a think bristled brush. When we used our own stuff it worked well.

Not easy to work with to say the least.