There are people out there that find it convenient to just do one click instead of holding three keyboard keys. Especially as you have the mouse in your hand while browsing anyway. That's the only reason why this Add-on exists. If you don't want to have a button in your toolbar (which, by the way, has the recently closed tabs as a list in its context menu), then you are right: In this case there is no need to install my Add-on.

Basically it is the same. The idea was to provide this feature as a button. I, myself, prefer to just click a button to restore a tab. I use the mouse all the time while browsing so it is always in my hand and it can be more convenient to click a button than pressing three buttons all at once.