I prefer using the running A’s for hip flexor and postural strength endurance purposes. The upright mechanics of a running A (and the ground contact time) will be closer to the upright running for a 200-400m run. But that is a personal preference.
Having said that, many 400m coaches have used longer hills (i.e. 300-600m hills) to build strength endurance. I have workout plans from Jim Bush that use hills extensively in the preparatory phases of training. I believe John Smith (who trained under Bush) also did this with his athletes at UCLA. They would run up the road that goes up behind Drake stadium.
If I had the right hill, I would use it instead of a sled. I do not like the feel of the sled as it tends to lengthen ground contact times and many people have difficulty selecting appropriate loads. Can it be used in lieu of a good hill? Certainly. But it wouldn’t be my optimal choice.