In the past couple of decades I have kept Achilles several times. They definitely don't like being captured and moving to captivity. But if you have a good home and they start to eat then they can do really well. My experience with both Achilles and Powder blue tangs is that they are prone to breaking out in spots - Whether that is ich, (white or black spots) or something else.
The spots come and go. The fish can look perfect for weeks, then is covered in spots, and then looks perfect again 24 hours later. I can't relate anything as to why or when the spots appear.
I have had no problem keeping Achilles with lots of other tangs. My best success has been starting with them medium sized when the orange spot is more of a sliver, and then letting them grow into the tank.
My Achilles was the last tang to be added (prior one before a major system crash, and new replacement at the beginning of last year). My current tang list is 9 yellows, 1 purple, 1 Chevron, 2 Hippos and the Achilles. We did have an Atlantic Blue tang that gave the young Achilles a run when first added. We rehomed the Atlantic Blue and the Achilles has done great ever since.
I do run a 2 story 26 gal surge tank, so the tank has plenty of flow for the Achilles.
I've only kept them in 300 and 400g tanks - So that may have helped with some of my success.
Dave B