Security, private keys; How much to you track me and my data?

Very clever software, certainly easier to set up than Wireguard.
Thanks for opportunity to use up to 100 nodes for free.
BUT, you must hold all the private keys?
So how much do you track my usage ( like Teamviewer)?
Can you see what I’m transferring?
If there was a software flaw, what’s the chance that some other account can see my data?
How much do you throttle the Relays? As you get more and more users won’t they slow to a crawl (like SyncThing)

The private keys never leave your own devices, so we can never see
your traffic. Much more detail:

We do collect some logs for diagnostic purposes, but nothing more than
you can see in the local syslog output produced by tailscaled. It
specifically does not track your Internet usage or browsing habits.

It’s unlikely that other accounts will ever see your data since to do
so, they would need your private key or to have data encrypted to
their public key.

We tightly throttle the relays, although this hasn’t been a serious
problem so far. Generally you want your traffic to not go through our
relays. The relays are intended only for situations where the firewall
is so strict that we can’t make a point-to-point connection between
your devices. In those cases, it’s better to have a throttled
connection instead of no connection at all. Note that even when your
traffic is forwarded via relays, it’s still end-to-end encrypted, so
the relays have no way to see the content of your traffic.