The only thing that is special about these plumbers is the hours they keep. They have all the training, skills, and equipment as regular plumbers, but they are available when the regular plumbers are not. This makes them essential when you have a plumbing emergency before or after their regular business hours, or even during holidays.
I'm glad that there are emergency plumbers should anything happen at some weird time or on a special day. Waiting when it comes to water problems can be disastrous. With these companies coming out right when you need them, they can prevent a lot of damage and extra expenses down the road.