To be honest i dont think the BMV thing will enlighten me any more than the dongle and app , I cant think of anything else which would require me to worry , as you know I run panels in series so if the day  is dull then I have the overvoltage to convert , it makes a fair difference on yield per day !
Also I have a 10 mile motorway drive to work and  then 10 back again when im done , I  park up in float every day !
Dongle/App gives you......
Panel volt/amp/watt in .
Battery  charge  voltage and amps going into it in realtime .  
Load being drawn as it happens in amps .
Maximum and minimum battery voltages each day .
Yield and consumption in Wh each day.
Max wattage in .
Max voltage in  . 
Percentage breakdown of Bulk , Float and Absorbtion per day .
Total power collected since first set up in kWh.
Now ask me again if I need any more data to mull over  
 
  
 