Security isn't a thing that you 'buy' or 'add', it's something that you 'do' and 'know'.
Using a VPN server and a VPN client doesn't do anything other than getting traffic from A to B over a presumed hostile network. Ideally using asymmetrical encryption to make sure the keys don't have to travel the network. Then, you sure probably use that tunnel to send all traffic, not just your p2p or http traffic. Using DNS over the normal network and your 'secret' stuff over the tunnel still exposes what you are doing and actually makes you more suspicious since you now look like you are trying to hide things (and doing a bad job at it). And what about firewalls, WebRTC hacks, routing tables etc. that now expose your network setup to any software you execute (be it an application or a webpage), or applications that don't honor your VPN setup and route packets wherever they want to. What about your OS routing stuff elsewhere? What about that Pi not being setup correctly and you happily using it but still leaking a ton of traffic over the visible network? A user of an easy VPN setup will not know and be covered by a false sense of security.
Even if you have perfect instructions and set it up perfectly initially, you would still be vulnerable down the road as new problems arise and mitigations might be available but unknown due to a user not actually knowing what it is or what they are doing.