It is entirely up to you whether you choose to upgrade your antivirus software. Specifically to Avast, we strongly believe in providing a
best-in-class free antivirus that offers our
core shields (which includes real-time and behavioral protection)
Many of our users do choose to upgrade depending on the features they are looking for. For example, we have an advanced and highly configurable firewall, an additional layer of ransomware security, and even Webcam Shield to prevent webcam snooping in our premium versions (features differ depending on which version you pick, of course!) A good comparison of the options is
here. With any of our options, you won't need an "additional" product to protect against malware as...