The pullover will work both back and chest while also using the triceps as a stabilizer.
The key to getting the most out of your pullovers is to pre-exhaust the target muscle, in my opinion.
I feel the Dumbbell Pullover more for chest, while I use cable pullovers for my lats. Doing pullovers for back at the end of your routine in the style of FST-7 (AFTER your back workout you perform 7 total sets starting with a weight you can handle for 15 reps, only take 30-45 seconds rest in between) really works well for size and width in the lats.
When I do my cable pullovers I will start bent over at the hips with my arms completely outstreched holding a rope together, as you pullover the rope stand more upright and squeeze the lats hard, then lean back down and stretch the arms back out.
Doing 2-arms works great in theory, but in my opinion the risk of injuring the shoulder joint outweights any possible benefit. The shoulder is not a ball/socket joint and it is very easy to tear a labrum or do other types of damage.