when I boxed I never worked out on a slip bag, but remember working on my head movement and head movement-footwork coordination with the two end bag, I didnt do it enough for it to be that effective but it helped i turned 30 and am going to start doing some light training again just to stay in shape which is a better investment for the garage
i think the double end bag would be your best bet, i've never found slip ball's good for much, i have a double end bag in my basement, great for working out little technique stuff. its a good thing to have at home.
