This isn’t an actual VPN but a DNS filter. As Android does´t have a way for applications to control the network of the smartphone in itself, most of them rely on the VPN connectivity, to be able to filter those connections.
I would suggest to actually follow privacytools recommendations, and requirements when choosing your VPN https://www.privacytools.io/providers/vpn/#vpn
However, if an actual free VPN is needed, It would suggest either to :
- Use RiseUp or Calyx VPN service which are maintained by non-profit organisations, and is maintained trought donations.
- Or, to use Orbot in order to redirect all smartphone network traffic trought TOR (Which is a bit more advanced than any casual VPN service)