Question About Rodda Sharkskin

I was wondering if anyone has had any experience with Rodda Sharksin. The manufacture info sounds really appealin, but that's commercialism for ya. We are putting in a new 600 SF deck using Douglas Fir (not ideal I know but it's what we can afford). I have been giving serious consideration to Armstrong/Clark products, but this Sharkskin stuff sounds appealing as well. However, I can't find much about it in terms of reviews, etc on line. Any advise is greatly welcome.

Also, I was wondering if there was any value to adding a stain to the underside of the decking boards. Might use a cheaper one and do it first before putting the boards down. Then wait a month or so and put the finishing coat on the top side after it has dried out. Again, any advice is greatly appreciated.

Thanks...

Jon