I see no mention of API use on the website, so it’s more of a privacy option for chat. That in itself is useful (no logging, no training on your data, encryption so Proton can’t see or share your data, no ads).

I tried Lumo a while back maybe I should give it a spin again if it's already included in my subscription

the upgrade from older to newer versions of lumo were definitely noticeable

Can you use it with pi or opencode etc?