I used the plastic green astro turf type outdoor carpet for a FasTrack layout I did. I really like how it came out.
I personally despise that plastic astroturf stuff. It looks terrible, falls apart, "flakes" come off, etc. I've used a very fine green out/in carpet and my current layout uses grey in/out carpet. I prefer the grey. I think it looks cleaner, a bit brighter, neater etc.
Mine has stood up to being moved twice, rolling out from and back under a bed for 6 years, and even cats scratching. And I use a vacuum to clean it. I've had no flaking or falling apart. Sure the cut edges can come apart, but I believe I hemmed it when I fastened it to the board, and then I just laid everything else on top.