Yes you can take all of the courses you like as a Gold member. Considering that being a Gold Member averages out to less than $5.00 a month (The price of a cup of coffee at Starbucks) this is a wonderful deal. If you decide after taking all of the classes you want to test out and be certified, simply hit the button, pay the fee, and take the tests. I like the idea that the study stones come to you via mail, if you decide to keep them you can or send them back and be refunded the $50.00.
I haven't taken any courses from IGA or ISG so I can't offer any comparison. Do your research and see what falls into your comfort zone. I personally like self study classes. Considering the vast amount of accurate resources available here I find it a good choice for me