Great question. The unit is pre charged for 25 feet of lineset . I was right at the limit for my install.
I installed the lines, did all the vacuum related work. Then just cracked the valve on the unit to distribute the refrigerant.
I had a bottle of refrigerant on standby from a buddy. Didn’t need to use it . I was going to get the EPA cert, if my buddy didn’t exist. I heard it’s super straightforward
The vacuum work, finding/fixing leaks, etc can be a real nightmare, even with the expensive equipment. Personally I would much rather pay an HVAC technician to just come and pull the vacuum. They already have the gear, and they can diagnose when your vacuum still doesn't pull all the way for the 3rd time. Then if you don't get a precharged unit, they can also fill it.
that is IF the technician cares enough... unless you guys have stringent regulatory/right incentives in place. sometimes tech just relies on the brand reputation and pull for 10mins calls it a day
Have few friends who got certificates in order to charge their