I have the older VCXDiag C6: http://www.chinacardiags.com/wholesale/wifi-bezn-c6-oem-doip-xentry-diagnosis-vci-multiplexer.html (the one without USB and ethernet on the side) and other than DOIP it has worked well for me with my May 2015 MY2016 W212 and I last used it about 8 weeks ago. I only use it personally on the one vehicle and not commercially though.
I don’t use the WiFi side, only ever the USB or ethernet cable – I tend to stick to the ethernet cable.
I never could get DOIP working – it passed the tests once in Xentry from 2018 with the manufacturer supplied HDD but as soon as the drivers updated it never worked again with that version and I spent hours messing around with it. I think they have an additional fudge in place somewhere to make the DOIP tests pass.
The supplier did say that the new disk they had would work with DOIP but I never sent this one back to test it – I should get around to it at some point. For now I just used a fresh Windows 10 64 bit install with Xentry 07.2019 and the VCXDiag drivers and Xentry worked.
I got the MB dealer to update my NTG5.1 in the end.
I need to use it later as I’m having some hesitations when pulling away, not sure if it’s a fault or just need to reset the transmission.