Am getting to know my newly acquired Octavia II and have bought a KW808 OBD2 which is fine. However, I see that there are Bluetooth OBD2s and wonder which, if any, are the most popular. Obvious advantage, as far as I can see, is that the module can be left plugged in and everything, at least in principle, is in/on an app.  I note that comments here on the OBDeleven reflect the potential unreliability or, incorrect operation, of aspect the app.

Thanks in advance for any helpful comments or suggestions.

A lot of the little Bluetooth dongles are not very reliable. 
 

I think the one which seems to get best reviews but is also able to scan all the modules (as opposed to just basic OBD2) is Carista. 
 

i have an OBDEleven myself and it was good to begin with but then reliability went downhill. 

 Many thanks, Andy, for your very helpful comments.

Nigel