I think the model o is the one that has a similar shape to the deathadder, which is 15 dollars brand new in the essential form. Its okay to try if you like that shape then purchase the model o and keep the essential as a backup mouse.
That would be the Model D that would share forms w/ the Deathadder (i have a Black Ops 3 edition Deathadder Chroma, decent mouse but about 3-5mm's too big), the model O shares similarities to Zowie's FK & S series mice. I like the shape but I want it a mouse at 118-121mm length for my comfort/accuracy for hand placement. The Superlight is closer but I can't be sure unless I try one out (of course I'd rather spend $150 on a GMK cap set but yeah, lol), and I know the Model O-/D- are nearly perfect in size but they need wireless versions (which I'm sure they're in process to being made - I would hope).
I own too many mice as it is - I have a hardware hoarding issue - DA BO3 Chroma, 2012 Naga, Zowie EC1-A SE white & Standard, FinalMouse Sream1, Rival 110, MM711, Model O, G403 Wireless, Flick G1 (best shape and size, just needs to be lighter), G502 Proteus Spectrum, Gigabyte DA clone, and my collector piece MSFT Intellimouse v1.1 (this mouse stays packed up in a box in storage).
I would love to find a good work/play trackball, I learned to play the original UnReal on a trackball/KB combo and imo it was amazing that way. I can understand why many move to a track for productivity/workflow purposes as you're not straining your mouse hand w/ constant movement away from your board/workspace. Also alot of programs work exceptionally well with them (AutoDesk and Adobe Suite - from my experience).
I'm sure they could help in coding due to the ability to stick close to your board etc.