Seems like we are saying the same thing, really. I read both manuals. Both say to add refrigerant by weight per foot of line set beyond 15 feet. Both also say to verify proper charge by superheat and or subcooling after start up. That is essentially what I said earlier.
I never said that it was the "preferred" method. I said manufacturers recommend weighing in charge on installation. PAge 6 of the Goodman manual says to. Page 14 of the Rheem manual says to. They recommend it both times.
Where is the discrepancy?
You start with the factory charge and line length estimate adjustment.
Then, you MEASURE. You adjust the charge based on that data, using the correct method, based on the metering device being used.
[Avatar photo from a Florida training accident. Everyone walked away.] 2 Tim 3:16-17