It shows a much finer grained representation of the whole transportation network. So you have much better idea of where is electricity produced and consumed within each country. When it comes to figuring out what the electricity mix is made of, electricitymaps is clearer.

They don't show the same thing. Electricity map is mostly focused on showing public market data about electricity and co2 emissions, while that site is a showcase of how a power flow works to calculate how electricity flows in the grid (not using real data of course, as the type of data used isn't public).

Both are interesting, I understand the site displayed in this article aims to show the complexity of the underlying system, which isn't shown by electricitymap.