I too had switched to a ball end T-handle wrench shortly after purchasing my Muscle Chuck in 2018. However, a recent phone communication with the people at Muscle Chuck said they DO NOT recommend a ball end wrench. There is a tendency for the ball end to "wallow out" the female receptacle.
That's news to me and does't make sense, I too was supplied with a ball ended key but it was springy so I bought the one shown in my earlier post and it has given excellent service.
Nothing but heaven itself is better than a friend who is really a friend. - Plautus