First the Scalp Comparison
My foremost criteria in shaving my skull is not closeness of shave. My wife isn't going to complain if my skull feels like sandpaper so closeness of shave is not my main criteria. I generally look for a razor that doesn't cause small nicks because scalp nicks bleed, quite a bit. My occipital bone creates a pronounced ridge that is difficult to shave and consequently it's a region that I end up nicking about one shave in three.
The Schick Quattro performs quite well by this criteria, it has half a dozen or so small wires that lie on top of its four blades. I believe that these wires are intended to prevent the blades from nicking the users skin and it seems to work reasonably well at the expense of a close shave.
The second criteria is how well the blade conforms to the varying curves of your scalp. Effectively what this means is how many passes you need to make to shave the same area because your scalp is curved and the blade is straight. Most blades bend or flex a small amount and I would rate the Schick as not very flexible.
Overall I'd say that for use on the scalp the Schick Quattro surpasses the Gillette Sensor variants.
The Beard Comparison
The problem for me with shaving both my face an my scalp is that I have conflicting requirements on my beard and scalp. I don't care about closeness of shave on my scalp I want good close shave on my cheeks. So the Schick Quattro fellates dead ferrets when your shaving your beard. It further does down on dead bears if you sport a goatee or other facial hair. The large chunky razor is unwieldy around the edges of facial hair that you want to maintain. I have two or three moles that I shave over and the Quattro while it doesn't nick them also doesn't cut the whiskers around or on the moles. Meaning you either have to pluck them
Overall for shaving your beard, the Schick Quattro was underwhelming to say the least.
Rinse and Repeat
The Schick has an interesting feature, the blades area back on a grid, the overall head is wedge shapped with an opening on the top providing a point for water to enter the louvres formed by the blades from the rear to facilitate washing the removed whiskers from the blade cartridge. This design works well except for the bottom blade. Given that clogging is generally a problem when removing scalp hair rather than the thicker whiskers on your face this is another in the win column for a scalp razor.
The Last Few Words
Overall the Schick Quattro is pretty good for shaving your head but really doesn't get my recommendation for shaving your beard.