I have loved working with this chip because the paralelism is so simple. Each processor works at a consistent speed no matter what. In low level robotics, timings is crucial. You can have one core positioning a bunch of servos, another core sampling ultrasound, another doing serial connections etc. For a cheap, simple chip it worked very well for a lot of robots I have built. I have used an Ardiuno Mega on a robot and while Arduinos have a lot going for them, it is difficult to control many things at the same time.
The problrm is that this chip hasn't really improved in seven years. Now the alternative is things like a Raspberry PI or other boards with cheap ARM processors which are much more powerful. A Prop is still great for I/O.