I don't know how you came up with this. I have fished Curados for years and there is no comparison. I quit using Curados when I started using the 50 Mgs. Sold my Curados on the flea market here. JMHO
Compare the schematics for the 50 Mg and the CU100b.
I compared the schematics of both reels and except for a handful of springs, washers and screws, the part #s are all different. They would be the same if they were the same parts. The common washers, springs and such prove that and a lot of those are found throughout the Shimano line. I don't want to argue. I have fished with both for years and they are not the same reels by a long shot. That's only my opinion for what it's worth. I won't fight about it. Folks who study the schematics and fish them can make up their own mind.
Ronnie