Nerwen:
When I was a kid (in the U.S.), we had Ovaltine, which we mixed into milk to make chocolate milk. I saw a jar of it in the grocery store here a few days ago. How's that compare to Milo?
Okay this is an answer from literally 5 minutes of google on the internet. I have never drank Ovaltine, so I can't give a full and proper answer.
With that out of the way
Ovaltine Malt and Milo LIKELY have similar flavors. Its hard to get an exact read here, because Ovaltine's reciepe varies from nation to nation.
However the following facts are true.
Ovaltine is more concentrated then Milo, and thus has a smaller serving size.
Ovaltine thus has more Malted Barley in it by percentage.
HOWEVER the main ingredient in Ovaltine is Milk Solids, where as Milo uses a filler (specifically Rice) which makes the Milk Solids less of a dominate ingredient in Milo.
So while their is less Malted Barley in Milo then Ovaltine, its the more dominant flavor.
The effect I suspect (and this part is PURE SPECULATION) is that Ovaltine probably disolves better in cold fluids (such as milk), lacks the delicious crunchy bits on top and has a slightly creamier flavor.