Merlin firmware is special in a good way. Merlin has a good relationship with the Asus firmware dev team, he gets early access to official firmware, they sometimes ship him unreleased routers. He often finds and fixes bugs and creates/adds new features that Asus pickup. Also very careful to maintain full compatibility with the stock firmware, making it easy to switch between stock and merlin. He has also created an interface to allow 3rd party features to get their UI page. There is probably more, but it really is an excellent project.