SD Connect C4 or Xdiag VCI C6 please?

[titof3b]

Hello everyone ...

I really do not know what to do.
I have a Mercedes Viano 3.0 CDI V6 year 2006
and my wife has a BMW Serie 1 year 2005

I have a problem with my Viano
and I wanted to buy a SD Connect C4 on China
and I also see that there is a XDIAG VCX C6

What is the difference?

with the SD Connect C4 I can read that Mercedes?

with XDIAG VCX C6 I can read the 2?

Mercedes and BMW?

can you tell me the best to choose please?

Thank you !