I had the option of a single 12, or two separate displays for the new boat. As I most definitley not a fan of combos, I went for the two screens. I went for the 9RVX (Pro) and a 7RV. Wanted two 9's but that would have meant going for two 9RVs. Extra width of RVX meant the second screen had to be a 7". The RV series, including the 12 you are asking about, is a lot less featured than the RVX Pros. You may have realised this already, but I'll sum it up

• RVX has 1kw built in, RV is 600w. You would need to add a 1kw module if you wanted that capability.
• RVX has Hybrid Touch controls, meaning that you have both physical controls and touch screen. RV is touch only. Do not underestimate this--pure touch can be a PITA at sea, with wet fingers and a pitching rolling boat. 
• RVX has dual card slots at front, RV has single at rear--hard to access if you flush mount.
• On paper , screen resolution is the same, but the 7 RV looks dull alongside the 9RVX.

As for the 3d, I don't think this is really mature technology yet. But their sidescan/downscan which is on the standard transducer is very good. I have the RV-100 transom mount xducer, and the picture doesn't go quite as far the the right as th left, no doubt due to the fact it is loooking past the motor at the shallower angle. I haven't used it out deep, but I have seen crystal clear pics from 70 metres. The 3D will apparently work down to 60 metres or so, there is a Kiwi video on Youtube showing this.  I tried my 3D in 100m, it lost the plot. The standard 600w sounder picture is OK, but not as good as the B175M 1kw CHIRP unit I fitted to my RVX.  

Overall,I am very happy with my network, which is the 9RVX, 7 RV, EV-100 Autopilot, and remote aerial. It talks to the Merc gateway, more or less, although Merc is the hardest to work with, at this stage. I can get an engine dashboard up, do fuel used and remaining, volts, etc. having the flexibilty to have either display showing whatever I want is very handy. 

There is a bloke on here who mounted the in-hull version of the RV ( RV-200?), he will doubtless add his impressions. Go to the Raymarine subf-forum on here, if you haven't already, and have a look at the content.

fishwrecked.com/forum/sidescandownscan-axiom-pro-shots

fishwrecked.com/forum/axiom-9-pro-b175m-ningaloo-sceenshots

fishwrecked.com/forum/axiom-9-pro-b175m-screenshots

fishwrecked.com/forum/new-install-raymarine-axiom-pro