Nice General Impression and follow-up discussions.
"
Maybe I'm completely wrong about BD, but from what I see I much prefer Emsisoft and Kaspersky."
"
I'm not so sure regarding its protections and also its bugginess is a problem."
I don't think you're completely wrong, but your preference is misplaced in this discussion as BD Free is, um, free where Em$i$oft and Ka$per$ky are not. Those two, of course, having 100+% protection and being totally bugless.
Never the word "fixed" in their changelogs.

In my expereince, BD Free is not buggy.
Your cons are real nit-picks and arguably valid, but "no firewall" is undeserved and might be considered a pro by many not running XP.
That a2hook32.dll is whacked for one of BD's partners' components is hilarious.
I do not agree that "BD Free is the minimalist AV taken to the absolute limit" if by that you mean "absolute minimalist." Especially upon consideration of the never-ending and dizzying array of "Free Bitdefender Engine!!" products, those without exception being THE
truly minimalist implementations of the bdcore.dll SDK and its supporting drivers and libraries. The "Free Bitdefender Engine!!" provides the threat database scan engine and B-Have heuristics, both of which have kept Bitdefender in the top three of the industry's Leader Board since that technology hit the market a decade ago. Third-party products may or may not include the Anti-Rootkit bdardrv.dll. Yes, it's in BD Free. (Premium "Bitdefender engine" products, i.e. Emsisoft, Ashampoo, Bullguard, implement a more aggressive, read: expensive, SDK - particularly the in methods available for scan.dll and trufos.dll.) BD Free's core is premium-class.
What those third party free products
do not have is the full-blown Active Virus Control which is available only in BD products, AdAware's paid products and eScan - to my knowledge as of this writing. Invented in 2010, AVC is their flagship behavior blocker. Running as a system device, BitDefender AVC HV, the process libraries avcuf32.dll and avcuf64.dll are separately attached to each and every running process. AVC monitors full-time everything active applications do for background tactics advanced malware deploys to hijack trusted applications. Not based on any single action, AVC keeps a running score and when, during execution or later on, a certain threshold is reached the process is reported as harmful. AVC's intelligence is supported by frequently updated binaries located in the AVC3 folder. (Source: active_virus_control_wp.pdf, published by Bitdefender and my own research.)
BD Free includes a HIPS User-Mode module (fwlibrary.dll), their Intrusion Detection System described on the Web site as "(Ensuring) that applications trying to access the Internet or the network are not masked malware." This is not to be confused with malicious URL blocking.
Speaking of that, the malicious URL blocking is a system-wide feature and not, as is typical, a component for "supported" browsers. I have tested its functionality in several browsers, installed and portable, and with malicious links opened in word processors and file readers.
A misconception exists that BD Free has received very little development with just a few updates, the last and current v1.0.21.1099 being cyber-ages ago: October 2013. The version actually pertains to its gzserv.exe version, the Gonzales cloud service - a polished, mature product that ain't broke. All other supporting libraries, drivers and services are updated in realtime. Should BD finally get around to, for example, a newer bdcore.dll, 11.0.1.12 will be replaced with 11.0.1.
new0ne. In checking the UI logs, you might occasionally see a "Bitdefender has been updated." In fact, the aforementioned avcuf dlls are time stamped 03/13/2105.
Finally, BD Free has the same priority to threat database updates as do the paid Bitdefender products. Though about 25% of BD Free's signature files are locally stored, considering BD updates
on the average every 1.5 hours, those 25% are always the latest. BD Free's unrestricted access to their Nimbus cloud network via the Gonzales service handles "zero-zero day stuff" as do the premium products and on-line protection for really old threats. That the premium product have the full threat database (about 900+ files) is to provide off-line protection for those really old threats.
Bitdefender Free has garnered a love-it or hate-it relationship with power users over the years, especially
very early on where there was no quarantine control for overly aggressive scanning evoking too many false positives, some of them system files. The current version is far more refined. Even Bitdefender is squeamish about it. Under the Home Users menu on their Web site, it's off on the right, far away from the For Windows category, under... Toolbox.
Anyone wanting a Bitdefender solution and unwilling or unable to fork over the payment needed, BD Free is unequaled. Because everyone else's "Free Bitdefender Engine!!" is not all-Bitdefender. Period.
All that said, 1) other free products (yup, Avira) are pretty doggone good and 2) whatever it is you paid for is better...
Cheers,
Ray Redbad
(Formerly FOXP2 at Wilders.)