hmmm... here's my take.
If you are really lusting over a J12, I'd honestly save up to get it. What may wind up happening is that your Technomarine, which is halfway there, gets worn a bit... then you see someone with the J12, and you go "Darn!!" I really still do like the J12. And then you become sort of self-conscious about wearing a perceived J12-wannabe. And you eventually upgrade to the real thing once you can make the ends meet. At that point, the Technomarine isn't returnable.. And why wear that if you have the J12?
If you are dead-set on a J12, try finding a used one. The good thing about ceramic watches is that they are really impervious to scratches. As such, a used one can look like a new one. With that being said, maybe you are perfectly fine with the Technomarine, as it accomplishes its purpose (black ceramic band, diamonds on face). If you just like the styling and don't care for the brand or exact design of Chanel's, just hold onto the Technomarine.
Most horologists do not take Technomarine very seriously, as it's a very nascent brand in the history of watches. That being said, Chanel was never a watchhouse either. I give kudos to Chanel for being a relatively new entrant into the market with the J12. It's done quite well, as is evidenced by the number of people I see wearing it and talking about it.