I would imagine (never having seen one of these) that anything smaller than "O" scale, it would be difficult to find material that would flow effectively out of the discharge chute.
Yo Toot:
You are right. Mantua, back in the day, before they sold the TYCO brand, IMHO, tried to duplicate the Lionel Line. The box cars, gondolas and flats were not only similar to the AAR 1937 car designs, but the Lionel product line.
When it came to "operating" or animated accessories (as they were referred to at that time); the HO stuff never lived up to the expectations, or the actual performance of the Lionel (and American Flyer) product.
That's why the "Introductory" products available during the Christmas Holiday Season, by Bachmann, TYCO, Life Like et all; were such disappointments to most people. the product did not perform as well as Lionel, or AF.
These HO products were never intended to appeal to serious HO Prototype modelers, instead, they were designed to appeal to the Hi-rail crowd desiring a smaller footprint than 0-31.
The Mantua "Tipple" hopper dropped some of its load over the coal trestle, but more often than not, didn't. On the other hand, the Lionel side dump always dropped its load into the receptacle, regardless of whether it was coal, logs or other material.
Joe