for right now it is limited to the available categories only listed inside of the product, but you should keep in mind that there are also many sub categories within the main ones listed.
It has many of the popular niche topics, and the list is going to be added into over time by Jon. Currently from the live webinar that Amin did the other day there are well over 1 million snippits and it has only just been recently developed.
My opinion on this product, is this: If, your looking for a soulution that can help you to create content on a variety of topics, and to help with the time process that this research would take, then this would be a very wise product to invest in long term.
If, you have your own niche topic, and if it seems like a popular one, you could also suggest this to Jon on the forum, and he can add it into the database of niche KW topics already in there.
Hope my answer helps to answer your question.