Welcome to Librarium Online!
If my Shas'o has a shield drone and joins with another Crisis suit team does the whole squad get the 4+IV** save?
Shield drones don't confer their invulnerable saves onto the models they are attached to, only shield generators do that. Instead they make use of the delegating wounds rules to prevent wounds from hitting the battlesuit, and may make use of the invulnerable save if something like a missile launcher or lascannon hits the drone only.
let me explain in detail how it works. Take for instance a two man XV8 unit with a Shield Drone. The unit gets hit and takes 4 wounds, 1 Lascannon wound and 3 Bolter wounds.
The rules state you have to allocate a wound to every model in the unit before any model can be allocated a second wound and every model must be allocated a second wound before any model can take be allocated a third and so on and so on.
Because each model in the unit is different (the XV8 are different because one has a Drone controller and Drone and the Drone has different a stat line to the XV8's) each model has to roll its own saves against wounds allocated to it. The XV8's cannot delegate any of its failed wounds to a Drone to survive.
So in this case the Lascannon hit would be allocated to the Drone because it has an invulnerable save (the owning player can decide which weapon hit is allocated to which model) and the two XV8's are allocated a Bolter wound each (because they can save against it). The final bolter wound is allocated to the Drone.
The Drone has to roll against the Lascannon shot with its invulnerable save and the Bolter shot with its armour save, if it fails any of the saves the Drone is removed. The XV8's roll their saves and if they fail a save they lose a wound.
The one good thing about the new wound allocation and Drones is any wounds allocated to the Drone are lost as soon as it dies. So you can allocate three Lascannon wounds to it and if it fails one all the Lascannon wounds are gone as well, they do not get taken by any of the other squad members. This is why it is good to have different models in units.
hope that explained things a bit for you.
Thanks guys made that nice and easy to understand
Might i also add that although it appears that shooting hasa been nerfed in my opinion it has helped the Tau as their standard unit of firewarriors all have the same weapon so there's no re-allocation problems. With XV8's we can then bend the rules to our advantage via different gear and drones and things so we don't suffer too badly.