Ok this: https://guides.getalby.com/user-guide/v/alby-account-and-browser-extension/alby-hub/faq-alby-hub/why-do-i-need-to-link-my-alby-account should clear pretty much all doubts, the Alby Account is the middle man to make everything which is public work, so they basically see all that is related to the getalby LN address if you link the node with the Alby account. I mean, it makes sense.  

 yep, albyhub is not about privacy, but self-custody. You are still trusting Alby + LSP provider with your transaction data/zaps. 

 Critical tradeoff

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