This suggestion is intended to solve the "free VPN app installs malware" problem and not solve the "VPN provider who actually logs/is in league with govt/MPAA/etc" problem.
OpenVPN is a protocol. If the VPN provider supports it, you set it up in your own client that supports OpenVPN. Using a VPN provider that requires you use some proprietary app is madness.
I recently signed up for such a service, in order to get my Nintendo Switch online for multiplayer gaming. My home internet connections sub-let from the landlord and could be considered semi-hostile -- not able to connect to peers on the Switch due to triple NAT, and I suspect some QoS throttling as well. The VPN solves my routing problems, but if anyone has a suggestion for another option here I'm all ears.
It is irrelevant what software the provider is using as long as they use the openvpn protocol. This will be obvious to anyone who tries to connect using openvpn.
To the client side or the server side? On the client side, you should download the code from a location you trust. On the server side, it is irrelevant if something is added to the software for the attack we are discussing.