it has been proven over and over that with extense heat and UV rays most of the syn do not hold up. Trex was pulled from our area and the vinyl's do yellow.
I am outspoken for natural products until they develope something that really does work. everyone is scrambling to market something since PT wood is about to go out.
Be careful and inquire about syn in your area that have been built and standing for a while and do check them out. A deck is NOT a cheap investment and IS one that should last for 15 years.