Ok so i've tested this Bitdefender Quick Scan add-on.
I've installed google chrome on my vm whit BitDefender QuickScan add-on
They i've downloaded 10 malware samples (5samples 0 day and 5 from 5days ago )
Run them and did a scan whit Bitdefender QuickScan :
Then to check the results i've done a scan whit Hitman Pro
And a Malwarebytes Quick Scan; Conclusions : If you want an on-demand scanner go whit an on-demand scanner like MBAM,A-Squared or Hitman Pro....not whit a browser add-on.