It depends on your situation and what benefits you’re trying to gain.
It’s probably a little better than just DNS-over-HTTPS and it may be a good option if you have a device which for example supports setting an OpenVPN tunneling for all your traffic but does not support that DNS option.
The biggest questions with these free services are how fast are the servers, are all the IP addresses blocked in most firewalls, do they work for the geolocation tricking one wants to achieve? They could potentially also sell your session window: connection time, disconnection time, IP address to the marketing companies but browser fingerprinting and other tracking methods are so advanced these days unless you use Brave or some other anti-fingerprint browser the marketers may not really have much need for that piece of networking level information.
RE: I suspect Mullvad VPN app might be to blame for burning my phone’s battery charge ...