Thank you for the kind comments!
@ Pat B: I think it s definitly worth a shot. Since I dont have (cheap) access to osage, it is my best alternative. In my experience, (very) good black locust can at least compete with average osage. It is a little bit problematic regarding compressing, but I have never had any problems with a flat or oval belly.
@240m3srt: I treated it with stain (sandalwood), which turned it a little bit into red. Without the stain, black locust looks even more yellow. In generell it looks very similair to osage.