Take the first item in yachtshop which is Clothing - this is a department group.
Mens and Womens, etc are departments in RMS and are grouped into the Clothing Department Group. A Megamenu is justified when there are a too many departments to display in your main navigation. The best way to decide if you need a Megamenu or not is to write out a possible hierarchy with a list the department groups and the component departments in each one.
Departments are laid out horizontally in a navigation menu on the home page. As you hover over any department link, the categories drop down and can be selected.
Here’s an example
When we mix hard-coded navigation links with either a supermenu or megamenu it’s known as a hybrid menu.
When you hover over the menu on bents, the green section on the left is static content. The white section on the right is their dynamic navigation.
Here are two examples
http://www.bents.co.uk/ - the items on the left in green are static and need to be hard-coded in - the other items in white are dynamic
http://www.meeksshoes.co.uk/Meeks - when you look at the dropdown for any department (Mens, Womens etc) there is a second list of brands to the right - these are all statically coded in