This is a bit of a holdover question that I never asked from the last edition, but as this part of the rules remain unchanged, I figured I'd risk of sounding ignorant and ask anyway.
"Stunned: Model counts as activated...Stunned models must spend their next activation idle to recover..."
The way I read this, whether or not the model has been activated in the turn it becomes stunned, it will be counted as activated that turn and then effectively miss the next turn recovering.
So, strategically, it would be best to make sure to activate early in the turn a model that you think may become stunned? Conversely, it would be best to target enemy models that haven't yet activated?
If I'm understanding that correctly, it would be the difference between that model getting to do something this turn or not. They'll likely miss the next turn anyway (or be killed of course).
At the same time, because charging a stunned model automatically kills them, I can see a strategy of charging a unit while they are down, before they can stand up and have the chance to survive another round of charging.
Further clarification question: If my opponent charges me, hits me, wounds me, and I roll all stunned results - am I immediately stunned and unable to strike back in that round OR does my unit get to strike back before being placed on its side?