For my opinion it's unsafe and illegal, if the CPT who occupies the RH seat is neither trained or checked for that.
What about SOP? In my company the go/nogo decision rests solely with the commander. He is trained for that. In a critical situation human being tend to fall in their trained habits. For a RTO there is a good chance that both will fumble with throttles and brakes.
What about SOP for CAT II/III ? In my company those appchs are done by the commander and the FOs head stays down on instruments until role out or even goaround. Would a CPT in the RH seat really do the tasks a FO is trained for? I don't think so.
I can't proof it by numbers but I have the impresion that statistics clearly say that accidents/incidents with a NONSTANDARD CREW (also Checkflights) are much more likely to occur.
No, thanks guys.