Well, it depends on the platform.
On the macOS, there are two product versions - a standalone (installed either from Avast web pages, or with Avast Mac Security) and an App Store version. The App Store version offers less features and it is less maintained, but it uses IKEv2+PSK encryption and thus connecting easier on the less stable networks. The reasons why the versions differ are mostly technical.
On the Windows, there have historically been two (pretty distinct) product versions. As much as I'm aware, the standalone version has been re-written recently and it should replace the bundled version, if it didn't happen already.