I've never once participated in this rare and not completely regretted it. It is not only terrible experience per minute, it is incredibly dull. The only way it could possibly be a good experience is if the party didn't mind my flower sniffing the zone while they did all the work with the rare. This rare ranks up there with the defending coyle quest (though even less exciting).
it is a horribly slow and tedious thing cause you need a full party to optimize the spawn rate, one or two people alone optimize the kill rate and you only need one person to afk hold the red name.
So you'd think others can go around getting kills elsewhere but it can glitch out the spawn rate at the portal and then someone will have to relog or exit/reenter to have the instance recalculate how many players are in.
The thing is the majority of slayer areas have just as many enemies per grouping or even more, aren't timegated by respawn timer and can have each party member contributing effectively at the same time.
GD is really only appealing because 5 out of 6 players can go afk and nobody has to run around...
Nevermind how often people will drop because they'd already got half their kills before you even started and then the spawn rate gets gutted til you get a replacement.