It does get a bit confusing and mainly because the way DJI put an interim upgrade option in place before the upgrade board.
The short answer is yes... the Upgrade board is all you need to run the Phantom with the Zenmuse. Does it make your Naza a v2? Well no, not technically.
Lets start with a real Naza v2. This comes with a PMUv2 module which handles power distribution from the battery as well as having a CAN-BUS connection (think of CAN-BUS as DJI's very own USB equivelent. It allows CAN BUS components to talk to the NAZA). It also comes with a seperate LED module but don't get hung up on that.
The Zenmuse kit comes with its own brain or 'GCU'. This is designed to plug into the PMUv2 via the CAN-BUS port when using it on a craft with the full NAZA v2 kit. The GCU connects to the Gimbal via an 8 pin cable (telling the gimbal what to do) and also has an output that can go to your FPV kit.
Ok now the the upgrade board. This takes over the functionality of BOTH the PMUv2 module AND the Zenmuse's GCU unit (both of which weigh the phantom down and bulk the internals up). If you only have a Phantom you literally don't even use the supplied GCU in the box if you have the upgrade board (you save that for your f450 upgrade lol
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Downsides to the board?... Well the only downside other than the soldering being a bit fidly is that the upgrade board doesn't have a CAN BUS port at all. The CAN BUS communication between Zenmuse and PMUv2 is handled internally on the board and hence no cable or port was felt needed). This means you cannot simply plug other CAN BUS items into the upgrade board like the iOSD min or Bluetooth module which you can plug into the PMUv2 that comes with the full NAZA v2 kit.
So it is not black and white and technically you are still a NAZA v1 but you have nearly all the functions of the NAZA v2 (once you dare upgrade the firmware of course).
Personally I would go for the upgrade board and if you've not bourght a Zenmuse get the NAZA v2 + Zenmuse + 450 (or 550) kit... that way you end up with a fully working Zenmuse ready Phantom AND a fully working NAZA v2/Zenmuse ready f450/f550. All for maybe a hundred or so dollars/pounds more than just the Zenmuse*
*you will need your own transmitter of course so factor that in.
Hope that helps
