I've been a mullvad user for the past couple of years. I only occasionally use them for privacy on open wifi networks or whatever, but the experience so far has generally been excellent. I initially used the official Wireguard iOS app to connect, but their iOS native app is freaking excellent. WAY more reliable and user friendly than the others I've used— ExpressVPN and some other. It's been quite some time since I used the other ones, however, and they may have equally good branded clients by now.