Been riding with these Surly cogs for over 3 years. I have three of them ~ 16 tooth, 18, and 20. I swap them out before a ride depending on the terrain I'll be on. The wider base of the gear does exactly what it's claimed to do. There are no signs of wear or damage on my freehub, and the cogs themselves still look as good as when I first bought them.
To be honest, I never noticed if they were heavy or not. After all, it is only one cog compared to an entire cassette. Only a weight weenie would take issue with these cogs. Everyone else will be pleased with the long life and no damage to the splines on their freehubs.