Are interview guides good enough to fully understand technical concepts?

Depends on the firm but for the most part the technical guides cover the generic questions you can expect twists from. Don't memorize but rather try and understand the intuition behind different concepts. Try practicing modelling. Once you can start to "visualize" changes such as different impacts on the three statements or valuation or something, then ur good to go. I recommend Rosenbaum and Pearl, pretty thorough and walks step-by-step through key concepts and provides examples.

Personally I had to learn to model to have any idea what was going on with interview questions. As much as I studied the guides and memorized things like how depreciation flows through different statements, I couldn't really internalize anything and would struggle if I hadn't seen a question before. Once I actually built some models it totally clicked and I was able to answer pretty much any question on any of those interview question lists, even if I hadn't seen it before. Definitely make sure you actually understand stuff don't just memorize questions.