Rossian, RAF Transport Command experience does not qualify one for commenting on airline ops. Being a commentator, broadcaster or journalist is often a disqualification; look at the usual pundits on BBC and Channel 4 and you'll agree. Only if he has airline experience does have some qualification to comment. I don't know him, so I am making no judgement.
As to whether the policy is beneficial, for most companies it is a hindrance, having to wait until a cabin crew member (who is not psycologically screened) reports to the cockpit, which often takes considerable time, and sometimes is too late, arriving after the aircraft is descending and the workload too high to safely leave the cockpit. However, some airlines played dispicably cheap with the regulations and only installed the armoured door, not the cameras for the pilots to see who is outside the door, needing someone to physically check through the spy hole (disgracefully, many are too lazy to do so), which obviously can't be done if one pilot is alone in the cockpit, so the cabin crew can do that check and open the door for the returning second pilot.
So, the policy's benefit depends on the company.