Opal drives are self-encrypting, so they’re done by the disk’s own controller transparently. The main advantage is that there’s almost no performance overhead because the encryption is fully hardware backed. The second advantage is that the encryption is transparent to the OS - so you could have a multi-boot OS setup (Windows and FreeBSD etc) all on the same encrypted drive, so there’s no need to bother with Bitlocker, Veracrypt etc to secure your other OSes. This also means you no longer have a the bootloader limitation of not being able to boot from an encrypted boot partition, like in the case of certain filesystems. And because your entire disk is encrypted (including the ESP), it’s more secure.