I will stick up for the OP in saying that the Reserve companion cert has recently significantly lost its value for me. In the past, as long as there was an A fare -- any A fare -- I have been able to book it using the cert.
Now that it is all through the system, you can go to book the A fare, yet when you indicate you are using the cert, the fare (still in A bucket) skyrockets and it no longer is worth trying to use the cert at all. I have tried it in numerous markets. Eventually you are able to find one where the A fare without the cert is not much lower than with, but that is rare.
I agree that the cert has very little value to me whatsoever. FWIW, I have never tried to use it to fly in Y, and wouldn't.