B737: Some have claimed it is better to arm both A/P in case of a G/A then you can perform a simple manoeuvre with the push of one button. I know of some pilots who made it their own SOP, until it was reported to CP and there was a summons to a meeting. There are some airlines that have it as an SOP, perhaps.
Those against this practice say that it is OK down to a disconnect at 500'agl and then, after the nose up trim input, it gets dodgy to land. Others say that the 30lbs force for nose pushing is a shock, but Boeing have no worries.
Indeed, in B767 sim, as part of LVO training and recurrency we used to practice manual land after A/P disconnect at low level. It was easy. But then you get some airlines that demand you execute a G/A if there is A/P disconnect <400' just because of the nose up trim. Not so comfortable if on minimum fuel and the disconnect/failure means either another circuit or a diversion, which might have been unnecessary. Why don't these airlines train the manoeuvre?
If you allow arming of both, then do you also stipulate a cloud base to allow disconnect >500'? Do you then allow only 1 A/P if cloud base is below 500', but that then leads to 2 different SOP's? Do you train landing with nose up trim and allow the PF to make the decision? No way, that is far too radical.
It is quite curious how complicated this can become. B737 FCTM seem to be a little light on direct instruction. May be someone on the inside can give a definitive policy answer.