Its more accurate than using google.com/trends, but Google Adwords isn’t very accurate either. According to the Adwords keyword tool, best casino and best casinos get a decent amount of traffic (but this certainly not true).
I like to use my own logic when trying to work out the best keywords, its usually pretty accurate. For example, you don’t need any research to know that “casino”, “casinos”, and “online casinos”, “online gambling”, “poker”, and “online poker” are very popular keywords. I like to target huge keywords so I know for sure I will definitely get traffic, and there is no guesswork about keyword popularity 