All will work, they just pull the air out of the bag at different speeds. The EC-4 pump is under 3CFM but works fine. However, if you are making large items such as body panels the larger CFM pumps are quicker but the smaller ones still work. However, large items can be problematic to get 100% sealed, especially if there are any sharp edges, so a bigger pump can cope with slight leaks easier. I know that all the videos show perfectly sealed bags but, hey, we live in the real world not in YouTube :-)