wow 29 bucks, that's a super handy dock for different hard drives.
You can get one of these to mount it internally in your Mac Pro. https://www.amazon.com/dp/B01LZWX6PD/
I never find booting into the OS necessary. It mounts as an external and you just navigate the HD to your user account and to the desktop or any folder you want and just drag and drop. No need to be booted in at all unless you want to use an app.Most of those hard drive Docks are great, especially when having to access Data on several different drives, but unfortunately, not all will work as a Supported Bootable Device, but one doesn't always need to be booting from an external drive.
Just a heads-up warning... but many do work when used as and needed as a Bootable Dock.
No need to be booted in at all unless you want to use an app.