Some people commenting on Heimdal don't seem to understand what it really does. Heimdal is zero-weight. Not because it doesn't do anything, but because of the way it works.
Heimdal runs a local encrypted DNSClient on the system, extremely lightweight. Then creates a loopback for DNS to the DNS Client on the 127 loopback IP address scope then forwards it to your normal DNS resolver from there after the DNS scanning and Heuristic analysis. This DNSClient is updated with the DNS databases from Heimdal Labs, which source from various non-traditional and traditional lists. This aspect of it protects your DNS from hijacking. (Smart DNS) It prevents DNS Snooping. It prevents DNS resolution for botnet/malware activity in the background. It also filters DNS for some phishing/malware domains. It does a few other handy things under the hood that are difficult to test. Not because they don't do things, but because they do things out of the experience range of most people that would test it, more towards network engineering.
So Heimdal IMO is a nice adjunct. ESPECIALLY for AV's that don't have DNS protections and/or lack proper firewalls, and/or have poor web filtration databases.. Since Bit Defender struggles in all of those areas, it would be a good adjunct to it.
@mekelek is 100% correct here.
Browser extensions are pointless in this conversation as they focus on web pages and they do not block network activity at all, and they only block after the data is already transmitted. Heimdal blocks on the network layer at L7, which is packet inspection+Application Layer Inspection. Adguard Extension works at L1 in comparison. That and it's nice to have an app that seamlessly updates your popular apps via a vetted repository. I disable Google Chrome updating in Task Scheduler and rely on Heimdal keeping things tidy and updated.
In tests, here, and in labs, Heimdal alone blocks in the range of 50-65% of threats, and since they source a lot of blocking from non-traditional locations (Darkweb, etc), they also pick up things other solutions miss. I have a layered system of protection here and at least once a day Heimdal is still grabbing something on some page. (malicious redirect, hijacking, miner, etc)
So in a nutshell, with your setup Heimdal would be very beneficial. On some setups, not necessarily.