If they are like the Crosman .177 Premier HPs, they will have too much antimony, resulting in a pellet that doesn't deform properly. Purely speculation on my part, and doesn't have much worth, since I haven't used the Benjis. I only use the .177 CPHPs for plinking, because they are cheap. I'd be more impressed if they (.22 Benjis) were a little cheaper, though!
Charles