Can anyone tell me, wether I should put a sim card into a slot of Superb or is the one in my phone sufficient for system to be fully operational?

Either works so it's down to preference. I'm using the sim as it's got a great data package and is always in the car. Using the phone works the same but you need to setup a hotspot each time (assuming you don't leave it running all the time which is a bad idea). 

So it's really down to the effort of connection. Aside from that they do the same thing.