Just to be super clear. If you ask the agent to recommend a soda and buy it for you, and it goes to Reddit, it is going to be exposed to prompt hijacking attempts.
As you can see in their marketing page, Muse is a personal assistant that reaches out and/or ingests data through apps, the web, your email/messages, etc.
If someone sends you a malicious email or if Muse finds a malicious website by accident, you wouldn't want it to send them all of your photos or to purchase things you don't want (or maybe that aren't even real).
The payment related examples on the page are of particular concern, but I imagine it kicks back to a human to actually pay for things. But who knows?