I get why Ranger and Tim decided to go with this shade of blue for Mermaid Lagoon. It is a bright blue without being in your face. At the same time is out of sync with the Distress line as a whole. I'm sure people will argue with me. But I want colors to work together since I prefer to use shades of a color family to create more interesting blends. Peacock Feathers was the odd man out, so to speak when it was released -- it just didn't work with any of the other blues and very few other colors. Mermaid Lagoon does work with Peacock Feathers, sort of. The two colors are at the same level of intensity, the same depth of tone, so when blended in layers they do not create something interesting. Again other people will have other opinions.
All that said, Mermaid Lagoon does something Peacock Feathers does not -- it stamps as a strong, clear blue. I prefer this color over all the other Distress Ink Pads for waves, blue roses, and other imagery that needs to be strong without being black or sepia. I know a lot of people use Salty Ocean instead, so it's my opinion.
I think there are better choices in the Distress line for a beginner, or for an occasional user. Nevertheless, Mermaid Lagoon is an interesting and useful color.