The main difference in my eye the feel of the mice. The DA uses a nice plastic that makes it look and feel high quality where the rival 310 looks and feels cheap by comparison. But! The Rival is also lighter by about 10 grams, so you take the bad with the good. It feels durable, but not nice and high quality like the DA.
Another major difference is the position of hump and how the mouse fills your hand. On the DA, its towards the middle and has a gradual slope towards the right side of your hand. The Rival has the hump towards the back, making the mouse feel fuller and bigger when you wield it. My hands are 17cm x 9cm and I found both comfortable to use and offer great control in my hand.
A smaller point, the clicks felt lighter on the DA than on the Rival 310, but I have no way to measure that. If there is a difference, its likely miniscule.
Hope this helps. Honestly, the Rival feels to me more like an alternative the final mouse S1 than to the DA Elite. Let me know if you have any other questions