Yeah I saw that video , I’d think sorting through frass is hard enough. Imagine adding bran to the equation ???Some people use bran as bedding for roaches but it increases costs and maintenance. If it gets wet, it molds fast. There is also potential for massive mite infestations.
DavesLilBeasties on YouTube has some videos on his roaches where he demonstrates his use of brand as substrate.
This is very helpful to the OP!!BEWARE
Some brands of 'horse feed' have chemicals. Equitrol or other brands, which causes male flies to become sterile. It may affect other animals. Also, many brands of feed have an enzyme based mold retardant. This is very common for nearly all livestock feeds that are intended to be stored. Very unlikely any of these retardants have been tested on exoskeletal animals.
And keep in mind, several brands of livestock feed have nicotine based chemicals to help control worms. Harmless to ruminants but is lethal to exoskeletal animals.
The reason why these chemicals are so commonly used is the health and safety codes. Lack of fly control gets a very hefty fine, public nuisance ordinance, and may get the animal keeper license revoked.