I had a 40DS for a while. Cool gun, definitely different, but not in a bad way.
I picked up mine, probably more out of curiosity and boredom than anything else, and it was available at a fairly reasonable price.
Mine shot well, and contrary to their looks, was very comfortable and natural in the hand.
DA trigger wasnt bad at all, and comparable to my S&W's. Not quite as smooth, but not overly heavy either. If youre used to shooting DA, you wont mind it. If youre a SA shooter, they all will seem heavy.
Recoil impulse is different, and if you shoot a couple of hundred rounds of full power loads, youll probably notice it in your shoulders the next day, especially if you're shooting thumbs forward with your arms more on the stiff side.
And a warning if you do shoot thumbs forward. That relief cut in the frame at the cylinder gap is something to watch. It seems to focus and accentuate that blast, and it brings it more rearward than other revolvers, and if your thumb is close, you will know it real quick. The tip of my offhand thumb got bit the first time I shot mine, and it got my attention real quick.
Ive never had the issue with my traditional revolvers with the gap at the top. Then again, the gap is at the top.
As far as what its use is? Same as any other gun, what you want it for. If I carried a revolver, it wouldnt be a bad choice. The gun shoots quickly and well, handles well, and can use moon clips for the reload if you want.
I shot this DAO at 10 yards, at a quick clip.
If you havent shot one, Id definitely recommend you try one before you blow them off. They are a little different, just dont let that scare you. "Fear is the mind killer...."