If you are wanting to use AirParrot to stream movies, and especially blu-rays, you are probably going to be disappointed. But the best thing to do is to download it and really challenge the app during it's trial. Throw your most challenging file (or flash video) at it and look for stuttering (jerky motion).
I have a 2009 MBP,2.66GHz duo core , 4GB RAM. It did not work well enough for me to be able to watch a movie. From my searching around, it seems the people who state that it works well for them have multicore machines and/or are doing simple desktop type mirroring or youtube videos.
AirParrot converts the video stream to h.264 on the fly which is extremely CPU intensive. That's why multicores work better. AirPlay on the other hand uses built-in hardware that does the conversion. Therefore, there is minimal load on your CPU and the hardware is hugely faster at conversion than software conversion (AirParrot).
But if you want, just give AirParrot a go and see if it fits your needs.