my observation from using both of these is: 'sling blade' has considerable less action compared to normal dodger, more of a subtle motion, it provides flash/color and put perhaps just a little action to the lure. sling blade also has much less drag in the water. I like to use them on my lighter gear for kokanee/trout, as an alternative to normal flashing trolls, with my lures/spinners about 24" back.
for salmon, I like to use a sling blade instead of dodger when trolling off a downrigger, side-planer, or when using a diver- they cause less false releases as compared to the more jerky action of a dodger...
Cheers, roger