Several people that I saw try, and fail the Series 66, before me used several course providers at the same time or to supplement. Not only was that advised against, it didn't work. While I was studying the Training Consultants (TC) material, I realized at a certain point that they were not going to teach me everything to be a competent IA, however, I would have a working vocabulary and know the right questions to ask in the future. At the beginning I thought that TC might not be explaining some concepts as thoroughly as I had wished and for those areas, I would look at Investopedia or one of the other providers. But then I realized, the reason why they may not get into super detail about everything is that you don't need to know it. And in practical terms, to pass the test, they are right on. So, sometimes my curiosity got the best of me and I wanted to know more, but the additional information I gained really didn't contribute to my overall performance. The TC questions, especially for Final Practice Exams 1 and 2 are of the same quality and difficulty as the actual exam. Although I didn't pass them on the first try, I noticed that I learned a lot from the explanations of why I got them wrong and did better after I went through all of the exams (1-5) and went back to take exam 1 again. I had the urge to try and take a practice test from another provider, but you really don't need more than what TC gives you. Just get through those well and try to pass them on the second time around if you need to. I would say that about 20-25 questions on the actual exam ended up being identical. Remember that they put hundreds of people through the course every few months and get continual feedback as to what the questions were like. So they are really up to date. I had the opportunity to look at other course providers material. For example, I heard that Pass Perfect works well too, but they take the opposite approach as TC. They give you everything! It is verbose and extensive. I know one person who passed and one who failed after two attempts with that program. The books are hundreds of pages and the questions are not similar to the actual test. One colleague passed using Fire Solutions, out of about 10 who didn't. I looked over the Fire Solutions material and found that it was way too wordy and they also gave you too much information. Again, the questions were not very similar to the test. Also, the webinars don't really add to the material. The executive summaries of what you NEED to know, aren't really that helpful either. I also looked at the Pass The 66 book by Robert Walker and it was worthless. He thinks that he knows how to right, but couldn't be more wrong. Ironically, in that book, the area regarding the USA, NASAA and IA Act of 1940 is in the very back of the book and that is what you need to study the most. Also, he fills his book with statements like, 'a security must be registered within the state, except when it doesn't.' Wow! Sage wisdom to live by. Some of this descriptions of investment strategies are okay but I would not drop $65 on the book.Lastly, STC's material for the 66 is also somewhat of a shot gun approach. They give you everything because they really don't know what is actually on the test. A colleague who attended their weekend course a few months ago reported that they admitted as much. Several who used the material said that it was too voluminous and failed on the first try. I heard that Kaplan was good, but have no experience with it. A colleague went to their two day course and passed and another went to the two day course and failed the test two weeks later. I guess taking the test closer to the course is more helpful. So, stick with TC, forget the rest, and use the support feature of TC to ask clarifying questions as they come up. I bombarded their support with them until I understood. Also, when you have to articulate the question, often times, you either answer it yourself or when you get the answer, it really sticks with you. Focus on the areas that are recommended to index card, highlight or that are in bold print. Lastly, create separate sheets/index cards listing the definition, exclusions and main points for each of the B/D, IA, Agents, IAR, Fed Covered IA, Security, Fed Covered Security, etc that you read about AS YOU GO ALONG through the book. I also made a sheet with columns to compare between the relevant terms. It is easier to see patterns emerge and memorize that way. Hope that this helps.PS: I would probably say that the above holds true for the Series 7 exam as well since I also compared the various providers for that as well.