My take is this:
As a child, I sucked my thumb. At the age of 5, my teeth were forming so badly that the dentist actually ENCOURAGED my mother to put me on a dummy. I of course, being steadfastly stubborn, refused, even when my mum put disgusting tasting liquid on my thumb, wrapped it up, etc. at night to keep it from deforming my mouth further.
I had to get braces at 12, one year after I stopped sucking my thumb at night.
Dummies, in my opinion, are much better. YOU control when/if they have them, they are quicker to get rid of when the time comes, and good for naps. If he's settling well at night, don't use one. But for naps, and other comfort throughout the day, great.
Also find dummies are great for when they're on an aeroplane or a busy train stopped in a tunnel, in the shop, etc and kick off. Quick, easy way to settle them for a few minutes just to ease the pain of everyone around you. But generally, they won't need them as much. Thumbsuckers control when they have it - can be better to find at night, but also worse because they fall into the habit and suck more and more throughout the day. Remember being humiliated in early school years for doing it.
Also, they make dummies that glow in the dark now, for babies to find them easier.