If your selling calves young (300-350) and at auction you'll probably be fine, by 500 the longhorn will be showing enough in conformation to affect your sale price. If you want to wean them and sell them to repeat customers you'll be SOL. Poor feed conversion and little to no finish will severely discount them to any feedyard, regardless of what you cross them to. Slower maturing is a nice way of saying they don't put on weight worth a darn. Longhorns have a place and someone needs to keep breeding them for the genetic diversity but your just
if your trying to raise a beef calf that is commercially viable.