Got one set up in my room, did 12 3s with a 30 second rest on it on new years day... wasn't expecting it to be as hard as on the bags because you're not pushing against any resistance.

But it's much harder pulling the shots back, when you hit a bag you have something to bounce back off... with the double end bag your shots just hang out there so you really have to pull them back in more. My lats and shoulders were aching the next day... Mind hadn't trained in a fortnight.

I start off just jabbing it, then I'll start one twos, after that I'll start throwing hooks after the straights so that the bag isn't moving into my fist... got time it and get your range right.

Then I'll just start putting as many combos together as I can.. keeping it creative... it's fun to train on because it keeps your thinking so it doesn't get tedius... try throwing a jab, pulling your right shoulder back so you cna throw your left hook... (don't just throw the jab and then loop your left arm... it's not really a combo, you practice getting the shot out there and then resetting your stance and shoulder as quick as you can that you can get the shot off, good practice so that you can throw shots quickly in sucsession with weight behind them... outside of having to throw a left then a right then a left then a right to be able to get the shoulders turning)

That's what made Tyson phenomenoly quick and powerfull... cus found ways of training him so his shoulders and hibs moved incredibly quickly, they had the muscle memory to snap back after every shot. I'll find some footage of a young Tyson shadow boxing and you'll see what I mean.