I have a question on the King.com website?

From what I can see, you can play for free, or you can spend a few dollars and get a membership. You can also play tournaments for money. However, the website information is rather vague as to whether this is legal or not. Basically "some countries can, some countries can't". You're expected to know the laws of your country. So -- can people in the US play for money? Also, has anyone done so and are there any pros and cons to doing so? Thanks for your help.