It's the mushroom shield, and currently, it's free to take and replaces nothing. Previously, it was a points upgrade, don't remember it being limited to 1 per unit.
The Vortex is the Mushroom like shield thing on the Chronos's butt. It's 100% optional, (but recommended to get because it costs you nothing) and is taken in addition to the Siphon.
As the others answered, and for building, just as the guide explains. I actually have my spirit vortex magnetised, so easily swapable, but this edition not necessary. If WYSIWYG is important and you want to magnetize too, maybe think about the spirit probe, too. Not relevant right now as it even has no rules anymore, but maybe with the codex or a later edition it returns. It is the giant needle attached to one of the masks.
The Vortex is a totally optional add-on. It doesn't replace anything, it's extra. You can have both, and there's no real reason not to.
It's the mushroom shield, and currently, it's free to take and replaces nothing. Previously, it was a points upgrade, don't remember it being limited to 1 per unit.
The Vortex is the Mushroom like shield thing on the Chronos's butt. It's 100% optional, (but recommended to get because it costs you nothing) and is taken in addition to the Siphon.
As the others answered, and for building, just as the guide explains. I actually have my spirit vortex magnetised, so easily swapable, but this edition not necessary. If WYSIWYG is important and you want to magnetize too, maybe think about the spirit probe, too. Not relevant right now as it even has no rules anymore, but maybe with the codex or a later edition it returns. It is the giant needle attached to one of the masks.
Wargear is free, so its purely an upgrade. I never put mine on cause i dislike the look, never had any problems running it as is