The arbiter is a high cost support unit. It relies on fairly high shield and hit point strength to survive, rather than its low powered direct attack.
It has a passive cloaking field that cloaks all nearby friendly units, but not itself. A popular strategy is to attach arbiters and observers to a carrier group. The carriers attack from under the cloak, and ward off attacks on the uncloaked arbiters.
The recall ability offers a powerful means of strategic movement. Arbiters may use recall to teleport forces into an enemy base, circumventing any defenses.