All that information seems to be inexplicably missing from all the explanations they are giving as to how this works.
Maybe that's something that will be released later down the line. It's almost like they don't want people to realize they are losing all security and privacy by using this.
All companies like their customers to be smart and educated enough to purchase their products or services, but at the same time ignorant enough not to question their policies and methods of how things are done. You are being a naughty boy o_e_l_e_o asking such things. 
Not surprising, spending directly from your hardware sounds too good to be true and it means you need to bring your HW wallet along with the Ledger card.
Too good or to scary. If you can spend the coins from a hardware wallet without physically confirming each transaction, who has your private keys, master private keys, or the seed phrase. That would mean Ledger has a copy of them.