I was so incredibly glad I bought the dot cards. Initially I baulked at the price but trying all of the colours and getting a feel for how they work (and how the work together) really helped me to narrow down my choices and pick colours for my travel palette that complement each other, ultimately saving me money. They give you a much clearer understanding how what the colours really are, as opposed to how they look on a website or in a YouTube video when swatched by others.
Also, there's something very relaxing about swatching watercolour paint. This kept me entertained for ages!