well Ive used Kaorti, Ethergaunts and Shari-kar
The etherguants got the least playing time, not sure if the players even saw them.
they had created a trap that would suck a single player into the ethereal realm, the players identified that it was a trap and avoided the bait.
I think their biggest problem is that they are too powerful, not a lot of ability to scale them.
The Shadri-kar were allies, from the plane of shadow, which fit really well in my homebrew.
The best was an NPC who was helping the PC elven druid, although the other elves acted incredibly bigoted and warned her against the S-K again and again. he was appointed was home sitter, and he did a fair job of it. Although she managed to avoid the more obvious problems, he eventually opened a hole into the shadow realm, in the middle of her grove. Mostly by refusing to believe what he was doing was wrong.
Not a bad sub-plot.
the Kaorti were the BBEGs of an entire campaign, seducing the PCs mentor into their ranks, and eventually only defeated by trapping the chairman underground for 1000 years, and creating a cyst destroying explosion, that left a 100' deep smoking crater. I think they managed to kill at least 2 PCs and a romantic interest. One PC was almost converted as well.
They win - hands down.