Doesn't work that well especially if you're higher level like me. Phantoms are super strong and sometimes the host will be a dick and use a seed even if it's 3v1. Real waste of time, imo. Messed around for a few hours but ended up just farming again. Basically got half from farming and half from PVP. Mound-Makers would be more fun if it was the Way of Blue version for invaders where you can easily team up to invade like coop. The red invaders could still do their own thing.
Well, I haven't really tried it late-game. I'm exploring The Cathedral of the Deep and done a bit of exploring in the Farron Keep, but already have maxed the mound-makers and gotten pretty far towards maxing the tounges just by invading a lot. And once I max those covenants I'm gonna do a lot more just because it's so fun. Basically, if I only have an hour or so to play, I prefer doing random invasions for fun rather than continue on with the game. Probably spent more time in pvp than pve.
But yeah, if you don't really like the pvp, doing it for the trophies only will probably suck. I don't care about the trophies and just do it for fun. Will probably never bother maxing the watchdogs and blue-bro covenants because they don't feel that fun for me. Why would I spend so much time doing something I don't really enjoy (farming mobs for covenant items because it seems really hard to get summoned to do those covenants the intended way) for some lousy trophies?