Ann: Corporate Presentation, page-13

Yes agree about impurity levels.
My understanding is spodumene sourced carbonate will be marginally easier to reach a suitable purity level due to differing contaminants.
Briners will either need a dedicated process to create a higher purity initial Li Chloride product or convert to a Carbonate of extreme specifications ie 99.9% targeting elements like boron.
These additional costs for brine producers in the Li metal market could level the Opex playing field with spodumene.
As always it really depends on the brine feed so is project specific.
This chart has a LCE intensity per KWh comparison for differing techs at the bottom.