mbed is great for prototyping. It's basically the Arduino system you would have gotten if Arduino was developed by people who mostly already know what they are doing instead of learning as they go.
Lots of libraries for various sensors and other applications, so if you do early stage development on hardware you can quickly throw prototypes together and not need to deal with sorting through a lot of mediocre Arduino stuff.
YMMV on keeping it for production use. Some parts of it should be fine for some applications. Other things not. I've run into issues with things like threads and timers not always working right for every library, but really that's par for the course on a system of libraries that diverse, and supporting so many different chips.
Lots of libraries for various sensors and other applications, so if you do early stage development on hardware you can quickly throw prototypes together and not need to deal with sorting through a lot of mediocre Arduino stuff.
YMMV on keeping it for production use. Some parts of it should be fine for some applications. Other things not. I've run into issues with things like threads and timers not always working right for every library, but really that's par for the course on a system of libraries that diverse, and supporting so many different chips.