So from the dimensions, their size is roughly the same..
How about shape?
When you do compare them side by side, they are almost exact in size although the DA2013 is cheap rubbish compared to the humble G400.
Also don't forget the weight issue here, if you are a limp-wristed baby, needing the absolute lightest mouse from these two - then the DA2013 wins as the most anorexic. But truthfully the G400 is better 'weighted' (if there's such a word) as you manipulate the beggar around your mouse pad.
The thing also affecting the movement of these rodents is the issue of cable interference. When I use the DA2013 it sometimes refuses to stay in a position due to the cable being caught elsewhere along the line, hence it basically moves when you step away from your setup. The G400 stays in position no matter were you leave it on your mouse pad because it has enough weight to cope with the cable trail that is left behind.
The other difference between these two rodents is the way you pick them up, the DA2013 is easier, because it basically is a direct rip-off of Microsoft's Earlier Shaped Mice (the best ever). But the G400 has it's own shape that you need to pay attention to, if you like lifting the thing up in the air and transferring it about your pad which might affect how you like manipulating this rodent.
One more thing is the position of your finger tips, they rest comfortably on the DA2013 whilst on the G400 they almost hang off the edge of it's shape, no biggie for me since I will palm the G400 easily. If you have a huge hand (like me) then the G400 might cause problems for you, but the size and weight of it suits me far better than the "Cheapie quality" DA2013.