The two listed above are good. I use the Blue Cat plug on occasion, because you can monitor down to -120 dB (good for removing unwanted frequencies during pre-mix). My favorite analyzer, Roger Nichols’ Inspector, is also free. You can monitor peak and RMS levels as well as panning/stereo spread. Part of the reason why I like it so much is because it’s about 1/4 the size of the other 2. That way, I can load it onto the stereo out and keep the window up on the side of my screen at all times without it really getting in the way. In terms of documentation, you won’t need much. Analyzers are pretty straightforward. The Inspector does come with a decent manual, but I’ve never really had to use it.