They are small, peacefull fish and are very worthwile to obtain if you plan on a PEACEFULL system. I introduced a McCoskers flasher wrasse to mine and soon realized this would not work, at least not if you want to see them. I prefer the yellows over the blue, The yellows are a little smaller and the color of the blue is more of dull slate blue and fades into the rockwork coloring too much for my taste. I have 2 yellows and a blue in a 65gal. these are thier tankmates. Pair of tru Percs, Red firefish, Tailspot blenny, Banded Hi-fin goby w/pistol shrimp, and a Mandarin goby.
With this combo of fish you can walk up to the tank at any time and most likely will see all of them. They are always out and about without anything in the tank to frighten them.
I have 16 other fish in a 210 tank as well and of all the fish I keep these little assessors are my favorite.