drabisan,Instant Guard may be easier to setup for most users and that's an advantage over OpenVPN.
Personally I don't see any reasons to use Instant Guard when I have a perfectly functional OpenVPN setup.
I may be wrong, but this is my understanding.
I agree that I will pick one type of VPN connection. For those of us who are comfortable configuring VPN ourselves.
Asus is trying to use Instant Guard to make it simpler setup and use Instant Guard VPN. For now, Instant Guard only support iOS and Android in beta ... macOS and Windows are not yet available, but, coming as mentioned by ASUSWRT_2020. For now if we need VPN on say macOS, we need to use other available VPN Servers on Asus Router.