I'll also note that if you start hearing the compressor too much, you can add more pag oil after the charge with it filled with refrigerant.
The sound it makes can be a sign that there isn't enough oil...
but it's more of a "feel the force" type of a thing for me as a novice.
I used one of these to add a tiny bit more oil to a system, it's pretty handy.
The way I use this thing is to measure out the amount of oil i want to inject, pour it into the tool with the valve closed.
Then hook the gauges up to it, hold it up to keep the oil in place but bleed some refrigerant out of the hose end to push out the air, then let it rip into the system.
I like to use it before the gauges so I can see the oil flowing through the window, that also allows me to flow into either the high- or low-pressure side if I wish.
This also allows you to inject dye if you need.
I currently have none in my system so if I feel the need, it's an easy addition.