It is basically two points of failure instead of one. Neither of them has the full picture on their own so they would have to collude to link you with your web traffic.
Discussion
I don't see it as having two points of failure. You're just shifting it, from Mullvad to Obscura.
Maybe I'm wrong, but I thought in this scenario obscura has your IP, but not the web traffic/public IP. Mullvad knows web traffic/public IP, but not yours. Neither knows both so neither can individually link an individual to their web traffic.
But Obscura can in principle relay my IP to Mullvad and then Mullvad has the full picture. So it is like a condom on Mullvad’s offering? 😁 Is that the idea?
Thats what I meant about collusion. In principle, they could do that. But the incentives don't really line up. Once that happens, business dries up.