As strange as it sounds, I am learning that currently (perhaps temporarily) an Ironwolf NAS drive in a USB3 enclosure would cheaper or same price as a WD Passport Drive.
Is there any technical reason or consideration on using or not using an Ironwolf NAS drive in a USB3 enclosure as an external drive.
No.
USB 3.0 has more than enough bandwidth, ~480MB/s for any hard drive which maxes out at ~200-250MB/s.