It has been said many many times "There are more variations within breeds, than between breeds." This holds true for longhorns, just as Warpaint said. If you are looking for BIG horned cows, you can find them. If you are looking for really meaty longhorns, you can find them. If you are looking for colorful longhorns, you can find them. If you are looking for solid colored longhorns, you can find them. If you are looking for something reminiscent of something found in 1885, you can find them. There are many different styles of longhorns, just as in other breeds. Whichever you like, and works for you and your program, can be found with a little research.
GENERALLY, Longhorns are more willing to eat roughages that other breeds are not as willing to eat. However, they do prefer nice lush green grass to browse (brushes, leaves, shrubs, etc...), and any ruminant will less desirable roughages if that is all that is left.
Ryan