On the powertop page of archlinux wiki it says:

There are two ways to automatically apply the suggested settings:

• Recommended: You can apply these settings at boot by using module parameters, udev rules and sysctl. For details, see the power management page.
• You can use the --auto-tune feature from powertop which sets all tunable options to their GOOD setting. This can be combined with systemd service to have the tunables set on boot. Remember to enable/start the service.

Currently I use the second method.

I have 3 questions:

1. Will the results be identical?
2. Why is the first way the recommended one?
3. How exactly to implement the first method?

Also, a comment on this post post says:

No need to install powertop, just install and run TLP. Feel free to check the variables in powertop afterwards, they'll already be activated by TLP. :-)

If I already use tlp does it mean that it applies the powertop sugegsted settings by itself? Or, to ask differently: do I need powertop if I use tlp?

On the TLP webpage there is a note:

On the other hand, attempting to run powertop --auto-tune on each boot may overwrite TLP’s settings depending on the actual boot order.

Is it a bad idea to apply powertop settings at boot?