For instance, lets say this is an on/off sorta thing- you use it, and it attacks the target until the target dies, you can't change its target without resummoning it, and it lasts until the target is dead. On a single-target boss fight with no switching, this is an obvious dps increase, we do 20% more damage, although you won't see big numbers. However, lets say we have Elegon- this raises the skill cap. You can, with keeping an eye on this, have 20% extra damage on each add, but since switching happens so often, youll have to direct it like a pet (Tanks generally have to help out our pet classes, because thier pets tend to durp and attack the boss rather then swapping to the energies). There is also the chance that you have to manually resummon it for each new add, which will REALLY raise the skillcap.
For PvP, a good question is, can the spirit's be damaged/CC'd? This would actually cause us to become REALLY interesting- we could spread out our damage amongst 2-3 targets, and easily swap focus onto any single one.
Either way, what it sounds like is a 20% damage increase single target, and the option to split that damage between 2-3 targets, thus causing TRUE "cleave"