I forgot to mention that I've re-assigned the video record button to the main button, as that makes more logical sense to me if you want to find record and keep the camera steady when hand held. I haven't got the cable release yet so I cannot try it. But it is a pretty poor show not to have remote start stop of video recordings. I have now seen that if I enable the ML-L3, switch to Live View video shooting mode, then go back and look at the remote setting, ML-L3 is grayed out. So it would seem Nikon see no logic in being able to start and stop video recordings with the ML-L3, when your D750 is on a tripod. Seems strangely illogical to me.
...And there's another thing: When you set the remote ML-L3 option to 'on' (whatever mode you fancy) It is NOT persistent. If you turn the camera off and on the remote control setting is removed to OFF. Can anybody explain what is logical about that? The D750 seems quite happy to shoot with the button or use the remote at the same time. When you have the D750 sat on a tripod you may want to shut it down to save battery and go off to lunch. When you get back you will have to re-enable your ML-L3 'on' option. But in the way most intuitive minds work, you will be pressing away on the remote thinking the battery has gone flat or you drank too much beer!