Hi there,
Please note that BullGuard does not rely only on the BitDefender's scanning engine.
We are also using a second scanning engine (mostly for Behavioral and On Access detection) and 3 sets of definitions, from which one is "home made".
The Safe Browsing and Spamfilter plugins include technologies from several world leaders in those fields, such as
Commtouch ( adopted by Google and many others).
The Firewall module is created by Agnitum, whilst the Vulnerability scanner (the ex Inspector) was developed with Secunia.
As a conclusion, BullGuard Internet Security uses the best technologies available for each plugin in order to provide the ultimate protection.
Hope this answers you question :)
Cheers!