odrive keeps your files as placeholder files until you want to download them, anyway. So even if File A was in 3 different places in Google Drive, you don’t have to download them 3 times. If you did, however, it would be treated as 3 separate files each taking up space. The mirrored files are still connected by the Google Drive backend, though, so deleting one of the instances of File A through odrive would tell Google Drive to delete it from that particular directory. Google Drive itself tracks the relationship as a mirror, which in the back end would effectively delete the file from the other locations. This would come back down as a delete in odrive in the remaining locations.
So I’d expect that even though odrive doesn’t treat it as a mirror locally on your computer, you still need to be careful since the Google Drive backend will continue to do so.
From a disk space perspective, odrive should overall be a net disk space savings (depending on your usage) since you can leave files you don’t use as placeholders. Especially with the Unsync feature, you would get granular control over how much local disk space is used.