I'm a little late. Sry. I have the D2 and the D3. IMHO, the D3 blows the Evic Mini out of the water. It is a yihi chip and I prefer tjhe menu TBH. It is also smaller than the Evic(not by much) feels really solid in the hand and hits harder - I find the Evic ramps up slower. I have zero isues with any of my batteries. I only use flat tops. I have LGs, Sonys, Imrens. All work perfectly.
As to needing a D3 if you have the D2 - well no. But I have numerous atties and RTAs and a few tanks. I like a mod for each set up. I was going to buy another D2 but when the D3 came out I jumped. I don't need upgrades. You can vape SS in TC if you set the temp for TI at around 200-215 at 45 watts and it vapes great.
I keep seeing the Evic mentioned as the best mod of 2015. I see the Crown hyped as the best tank. I think both are good but neither are my favorites. I guess I'm different. My favorite RTA is a haze dripper not my bellus, not my aromamizer and not my zephyrus 2. My favorite tank is my triton 2 - yes you heard me right. I can use the vaperesso ceramic coils in it. It tastes great and blows enough clouds for me. I also prefer the smok vct tank to the crown or TFV4. I hate the TFV4. Just traded it for a mutation RTA (in the mail still). I gave my son my crown.
My point is that preferences differ. These are just my preferences. I don't judge by hype but by my personal tastes. I had the velocity mini and traded it away. I was the only guy at the vape shop that was not a fan, lol. I prefer my comvape products - twisted and double vision. I love my phenotype. I enjoy the heck out of my hannya postless. I watched a few videos of the best RDAs of 2015 and only the twisted was mentioned and it was number three I think.
So yes, I would pull the trigger on a D3 in an instant. Love that little mod.