Black locust does have a thorn, just about the same size as a hedge thorn.
Hedge (osage orange) is THE durable post. They DO grow strait. Just cut the wiry ones up for firewood. That said, I do use locust posts. I just don't put them where I want absolute permanence. Both species make excellent firewood. Hedge is better for a closed woodstove, however, as it pops and sparks somthin' fierce.
Swampdweller