Range pickup's are fine you need to monitor the brass for cracks, bulges and loose primer pockets no matter where you acquired the brass.
Keeping new brass in it's own lot is always a good idea just as I think sorting by head stamps is. Not all brass is the same nor do they all have the same lifespan. Even if you sort them by brand and head stamp you won't know the age of the cases so keep a close eye on them.
I think the manuals all point you in the safest possible direction even though many that have reloaded range pickup's for decades don't hesitate loading them after sorting and inspecting them.
NRA Life Member, SAF Member