This is a different flavor of the breather/PCV/catch can discussion that has gone on many times here...
In Ford engines one side will be mild vacuum and the other side positive pressure outbound. The pressure side is the side on which the PCV system resides to direct the "exhaust" back into the air breather assembly (somewhere) where it goes back into the engine.
Catch cans are, with rare exceptions, just income to the producer of the part. They serve no useful purpose. The amount of
oil "blow by" captured is drops per 100 miles and will do nothing to reduce octane. If they were an important part of the EPA gas rating of engines trust me they'd be there from the factory.
The joining of the two sided nature of the covers is why there is no value in having two catch cans.
With two exceptions...
First, racing and continued operation at high revs does produce some blow by. The amount is still inconsequential to engine operations.
Second, if you have excessive blow by, and if you have virtually any in the vacuum side, then that is the sign of a much larger engine problem than a catch can can solve. Especially if you have a naturally aspirated engine.
I understand that some recent model year GT500s have catch cans as do (unconfirmed) the higher end versions of the Challenger, but noone can verify that they collect other than miniscule amounts. Note both are supercharged applications.
My Kenne Bell equipped Shelby GT had a catch can that never saw any
oil and it wasn't because I drove it like an old lady. The later Ford/Whipple version did not include one.