I was curious about this, and when the price dropped to $10 I decided to give it a whirl. It's a good raw converter, but despite the "Pro" in the name, offers only basic functionality. It doesn't have all the features that you'll find in Adobe Camera Raw or other high-end raw converters, and it's lacking some basic usability features like a numeric indication of colour temperature and a way to set the zoom level other than a cumbersome slider, but hey, it's only $10.
The thing I like most about Raw Converter Pro is that it does not apply any automatic lens corrections to images shot by cameras that rely on software to correct for lens distortions. One of my cameras is a Panasonic LX3, and using Raw Converter Pro I can recover a lot of extra pixels along the edges and particularly in the corners. I then get to choose how much (or how little) lens correction I want to apply in Photoshop. So despite its limitations, Raw Converter Pro has a place in my workflow.