The only difference between these 2 unit is that the HD version is the new 2013 model that has an LED backlit screen which improves the sunlight visibility. The non-HD version is the 2012 model and all other functionality is the same.
Just an FYI....That online store that calls itself Humminbird Factory Outlet is not affiliated directly with Humminbird. They make it appear that they are Humminbird. Do a Google search on them and you won't like what you find. They are a big warehouse store in New York and get a LOT of bad reviews.
For an online purchase, I would stick with BBG Marine or Universal Mania. They get good reviews.