The DIY kit upgrades the TX to a level beyond an already competitive radio. It puts it in class with radios that are WAAAAY more expensive (JR, Futaba). It also adds a backlight and some aesthetic upgrades.
Now, before I make myself sound too much like a schill for Parkeflyer, I am merely a very happy customer. I bought the stock Turnigy 9x about a year and a half ago (this is the same radio as the link I posted, but branded under a different name), then sent it to Parkeflyer for an upgrade. The capability of my radio is far above what I had before. That being said, it was already a very capable TX in its stock configuration.
The DIY kit gives you what Parke did for mine + more. But, I don't think you need to worry about that at this point in your RC hobby. You will be quite happy with the stock FlySky. While I don't fly multi-rotors, I am certain it will handle them just fine.
However, if you were to upgrade to the er9x firmware (DIY kit), you won't have to relearn your TX, as I am doing now. And if you are interested in going into fpv, you might consider purchasing the Frsky Module. It is telemetry capable and supposedly has one of the best, if not THE best reliability of any system on the market.
This is A LOT of info to digest when getting into the hobby. You don't need anything above the base FlySky, at this point. If you email Parkeflyers customer support and tell them where you are at and what you are interested in, they will give you an honest response. Case in point: I broke the antenna wire on my tx this week, less than one week from receiving it back from Parkeflyer, and Thomas's advice was to just find any 2.4 GHz antenna in lieu of purchasing a new module from him. They really are trustworthy guys.
