Simple UI: Most utilities are available from the main screen, with little need to jump menus and screens. This helps users maintain focus on their project while enabling access to tools that they need. The ability to increase and decrease the spectrogram intensity on the fly via hot key also helps.
Useful features: Capo displays guitar chord diagrams as the song plays, which can be edited on the fly. The quick access to tempo and pitch change on the bottom-left corner helps you break down music at your own pace. Advanced users can take advantage of region selection tools, thanks to the ability to color code and label areas with complex riffs. Additional tools are available to help isolate vocals and other sound layers.
Small learning curve: Intro videos help you quickly jump in and get introduced to features, making it friendly to new and experienced musicians, alike.
Variable performance: Much of the chord and note detection depends on the quality of your audio file. Music with muffled chords and complex-layered synths might not always be detected, perfectly. You can remove vocals, though.
Small UI: The spectrogram timeline is very small for adding individual notes, without the ability to scale note lines.
Capo 3 is a superb tool, overall, and does a lot for a small, lightweight app. It can be extremely useful when placed in capable hands, but thankfully it doesn't require you to be classically trained as a musician to get a lot out of it. The focus of the app revolves around the spectrogram, which helps you visually determine the right chords, though the built-in chord detector works great if your sound file is of high enough quality. It's not perfect when it comes to pure detection, but for someone who's trying to reverse engineer their favorite song, it'll take them a long way.