I have not had any issues with the j hook. As with the knaider, if you have weight on it, you can't lift off. I have not had this happen yet but if the WE step is not locked on flat, there is a possibility of the hook sliding left or right. The same is true with a carabiner but the j hook may slip off and the carabiner would not. I have not decided on the j hook for certain but I wanted to try it and so far I prefer the ease of just setting the hook over the bar. I also plan to have a bungee to my lineman loop in the event I drop it or it does slip off.
Where did you get the j hook?