I tried using them years ago. Several things I found:
1) The Hobart rods where the worst to use. They did not work well in any condition. The best one I found then where Forney rods. They where not great either.
2) You have to preheat the aluminum before you have any type of luck at all. Then the penetration will be better.
3) You have to hold your rod at almost 90 degrees to the weld. Not at the lower drag angle like you usually do. It almost is like running a vertical down in a flat position.
4) I found that my DC portable welder did a much better job than the Electric buzz box DC welder with them. I think the buzz box welders do not really put out the correct cycle in higher amperage conditions. I know cycle is not the correct term but I can't think of a better way to explain what I say happening. The Portable just ran the rod smoother. Now that is not really right in that the finished product looked terrible.
The aluminum stick rods just prove that a MIG or TIG machine is the better ways to weld Aluminum. It just takes a different environment than a stick rod/welder can provide.