For pvp it's pretty nice, pve not so much.
Taking 10% away from a 40k hp warden, while also reducing their healing is not bad for a single status effect.
I sometimes use it in PvE on trash pulls with the Blackrose Prison lightning staff as a tank, but it doesn't do that much and isn't really beneficial. As others have said, Minor Mangle is better used in PvP rather than PvE.