Jeff:
This is good advice. The only issue would be that the golf grip is different from the pool grip in the angling of the wrist to the instrument. (And let's not forget you're swinging a golf club perpendicular to the gripping area of the instrument itself -- a la baseball bat style. This is compared to the "swing" stroke parallel to the grip that one would use with a pool cue -- sort of like an underhanded javelin or spear.)
There are almost as many different grips as there are hands to implement them. I agree with The Renfro that certain individuals, because of the sheer size of their hands, if they tried to point their thumb perpendicular to the ground, they would have to arch their wrist outwards to do so -- sort of a Keith McCready sidearm grip, except without the sidearm itself. If this is not comfortable, it's not conducive to being automatic and natural, and is therefore wrong -- for that individual anyway.
Rather than focusing on pointing fingers and thumbs to the floor, how about instead approaching the grip from the INSIDE surfaces of the hand? An old-timer once told me about what he called the "sock puppet grip". At some point in their childhood, everyone's donned a sock onto their arm, and made a puppet out of it, right? You know when you use your first knuckle of your index finger and your thumb to form the upper and lower "lips" (if you will) of the puppet's face, arching your wrist ("flexion" according to The Renfro's diagram above) to orient the "face" correctly? That same movement -- where you pinch your thumb's knuckle upwards towards the index finger's first knuckle to make the puppet's "mouth" move -- is the grip referred to by that old-timer. (But obviously, you're doing it with a straight and not flexed wrist like you'd use to make a sock puppet.) You're basically "pinching" the cue between the side of your thumb and the first knuckle of your index finger. In effect, this is the "clamp" that holds the cue, leaving your fingers free to open and close in unison with the pendulum motion of the cue. Think of it as a bolt that goes through the first knuckle of your index finger, through the cue (laterally / horizontal to the ground), and through the side of your thumb. You pivot on that -- both sides of the cue -- like a hinge. It also gets rid of the dreaded "grabby grabby" motion of the fingers, encountered most often with a faulty cradle grip -- which often throws-off the cue delivery. (I say "faulty cradle grip" not with the intent to say cradle grips are faulty, but rather that many folks, when trying to implement a pure cradle grip, *tend* to bend their wrist inwards to form that cradle. This causes the wrist to impart a "hook" in the delivery.)
When the grip is approached in this way -- using the interior surfaces of the hand as a guide, and not the orientation of certain digits -- the grip is more apt to be oriented correctly in relation to the wrist and arm.
I hope this is helpful,
-Sean