PCMag shows an aggregate AV test lab score of 5 for BitDefender Free.
BitDefender Free has never been tested by any AV labs... ever... as far as I can find.
In any case, the argument is the BitDefender Free uses the same technology as BitDefender's flag-ship products.
While that may be true, I remain unconvinced of BitDefender Free's capabilities... maybe it would have made a difference if it would work correctly on my W8.1 AMD system.
If I had to choose one from the comparison, it would be Avast! Free.