Anyone who has your extended public key can see all your transactions, anyone who has your silent public key sees literally nothing. That is the difference.
Sure, but you're supposed to hide it, just as you hide your private keys. And if you don't trust your web hosting service, which is normal, you can make it contact with your home's server. Such as Pi <--> Web hosting' server <--> Sender
Either way, you need to run your own node and scan for every transaction.
Previously, Alice had one address with many outputs created by different senders
No, I mean the idea with the master public key. No address reuse.
Let me show you.
With master public key:
┌───────────┐ m/84'/0'/0'/0/0 ┌────────────┐ bc1q8g4...fjyjy ┌────────────┐
│ Home node │◄───────────────────►│ Server │◄──────────────────────►│ Visitor #1 │
└───────────┘ └────────────┘ └────────────┘
┌───────────┐ m/84'/0'/0'/0/1 ┌────────────┐ bc1qeud...ccr6f ┌────────────┐
│ Home node │◄───────────────────►│ Server │◄──────────────────────►│ Visitor #2 │
└───────────┘ └────────────┘ └────────────┘
┌───────────┐ m/84'/0'/0'/0/2 ┌────────────┐ bc1qwzx...2dxz7 ┌────────────┐
│ Home node │◄───────────────────►│ Server │◄──────────────────────►│ Visitor #3 │
└───────────┘ └────────────┘ └────────────┘
Et cetera.
┌────────────┐ bc1q8g4...fjyjy ┌───────────────────┐
┌──────►│ Visitor #3 ├──────────────────────►│ Construct Address │
With silent payments: │ └────────────┘ └───────────────────┘
│
│
┌────────┐ bc1qw8sz...kk7qu │ ┌────────────┐ bc1qeud...ccr6f ┌───────────────────┐
│ Server ├───────────────────────────┼──────►│ Visitor #2 ├──────────────────────►│ Construct Address │
└───┬────┘ │ └────────────┘ └───────────────────┘
│ │
│ │
│ │ ┌────────────┐ bc1qwzx...2dxz7 ┌───────────────────┐
│ └──────►│ Visitor #3 ├──────────────────────►│ Construct Address │
│ └────────────┘ └───────────────────┘
│
┌────────┴─────────┐
│ Scans the chain │
└──────────────────┘
The result is the same. Alice has received donations in several addresses, that have no connection.
Advantage of silent payment would be if Alice receives many payments and cannot reply to senders.
She doesn't have to reply to anybody. Address generation can happen automatically.
It would be more interesting to hide sender, not receiver. Maybe silent payments together with help of miners can break connection with senders.
Use a mixer then, end of story. No need to complicate it with miners and coinbase transactions.