It makes the raid quicker once you reach the sisters and Oryx. I've seen some people use it in earlier parts of the raid, but it's especially useful for the last 2 boss fights because of the immortality auras. You can spam the last shot without killing yourself and get an insane amount of dps.

That makes sense, but I still don't see why it's a requirement. If you have it, use it. If you dont, use the best you have. I have both black spindle and eirene from the gunsmith but I tend to use eirene much more. No one in the raid had a problem with my using eirene and we downed every encounter up to the sisters in one try. The raid leader, who was skeptical at first because we were entry level light and complete raid noobs finally told us he would raid with us over some of his regular group any day. If you have a solid team who listens, coordinates, and communicates well, you can do the raid and maybe even "easily". My friend stayed on and beat Oryx after I left to get the achievement. He said it was about the same as the first half of the raid in terms of difficulty. Honestly, I found the hardest part up to the daughters to be the freaking bunny hopping across the bells, the ships, and the catwalks.

Yea, honestly I went for it to add to my collection. I didn't know what the fuss was about until I used it. From my experience, when you let your team play with how they're comfortable playing and the skills they've mastered with the weapons they're good with, you usually suceed. Outside of asking someone to change classes for add duty or dps support, I don't know why some gamers want everyone to play the same or force requirements. I've seen players do things that make me go, oh no, but then when they suceed, I'm like, huh, never thought about that. It's fun to see how many different ways people have found to tackle the same thing. I like the diversity. It's what keeps the game fun.