I don't think you will find it written.
In final approach (wether NPA or G/S capture from above) it is definitely wrong to use OPEN DES.
But in other stages of the descend there is nothing wrong with the mode you use as long as your parameters are OK. You can have too high a sink rate and idle thrust with V/S green on your FMA, as well as with OPEN DES.
One thing I don't like about the OPEN DES mode is the rate of deceleration after selecting a lower speed. Sometimes it takes ages! It is far better to do it using V/S rather than accepting the result of who knows what algorithms in the computers, whatever it is. It gives more control.
Another problem (potentially disastrous) of this mode at low altitudes is if we fail to switch off one FD when the PF says "FDs OFF" (it can occur and remain unnoticed for several reasons such as distractions, fatigue, etc...). Then we have A/THR active in THR IDLE and not SPEED.