Great overview of covered hoppers. These indeed became very popular when they were introduced, because previously loose stuff such as grain and sawdust was shipped in boxcars, which must have been a pain, not to mentin messy.
I would note that the ACF-type open-sided hopper was also built in a ten-hatch version. I couldn't find one off-the-shelf, so ended up modeling one for the B&M by using an eight-hatch Weaver, plating over the roof, and using thick styrene for the new hatches.
