I've used C++ Builder for some time and it is quite good but I also use Visual Studio when I need to develop some C++ code.
Now, for RAD Studio, the capabilities are really great requiring the minimum efforts by developers in order to create native cross-platform apps (Windows, Mac, iOS, Android) with no cross-compiling or wrapping around the code. That is really great but when it comes to price, the cost is prohibitive for single developers / small companies and it is somewhat expensive for even bigger companies. The license (of some thousands dollars) purchased with RAD Studio is not exactly perpetual as it does not include upgrades (which are about once per year) and technical support although great, is somewhat expensive too. I don't say that the total costs included are unreasonable given the power of RAD Studio but the whole thing is somewhat overpriced.
For its usage, as far as I know, it is advertised to have around 3 million users worldwide. In my country I know quite a few people using it in the companies they work for.