What else can I get with 500 coins? Like a ft ak redline? Or usp guardian or smth?
You would have to check, you can either get something up to 500 coins or bet those coins on the main site to get more coins and get a better skin. That was just an example! 
Which means, no. U can try but the results wont be that good

If you want you can get that skin and play poker, RPS battle, blackjack, where you are sure that its fair.
Honestly, I never trust those sites, Ive lost 11 times in a row with a 40% chance to win, multiple times on multiple sites.
But, ye, up to you.
Btw gj for sharing this with us.