The other thread got a little off-topic, so I think it's best to start a new one.
I've played with Topaz Clarity for a few days now, on a wide variety of images. I've compared Clarity to a number of "contrast enhancement" and "tone mapping" techniques I have. These include "parametric" techniques using a range of custom luminosity masks with Photoshop levels and curves.
My conclusions and some samples follow:
1. I like it and will add it to the toolbox. It's definitely different than the other programs and techniques. Much different from ACR clarity. I suspect Topaz is using some advanced frequency and luminosity separation techniques. But I have a number of ways to do those separations and none come close to what Topaz Clarity does. The only way to duplicate what Clarity does using Photoshop only would be to spend hours on pixel level dodging and burning.
2. By different, I mean just different. Not necessairly better or worse. There is a lot of personal taste involved in this type of processing. I prefered the results of Topaz Clarity on about 75% of my tests. I prefered it over ACR clarity on 100% of my comparisons.
3. I focused only on the "Dynamics" function. I took a quick look at the Hue/Sat/Lum controls and found those sliders to be "sledge hammers". Way too sensitive. Of their range between -1 and +1, only adjustments below 0.25 were usefull or needed. Plus, I've got a lot invested in advanced saturation techniques within Photoshop, so I'm not too interested.
4. Ditto with the masking. It looks interesting, but the lack of a full sized mask preview makes it difficult for me to use. Especially if trying to trace an edge. All you can see is the mask thumbnail. Plus, with the advanced masking in Photoshop, I'd rather let Topaz process the entire image and mask later.
Here are my samples. I chose this image because I wanted to bring out the fine and subtle detail in the plaster wall, and that's a good test of the techniques. Yes, the original looks a pretty flat to begin with. But that's because the light was very flat that day. But if you look at the histogram of the original you will see it spans the entire spectrum with no clipping. Just trying to apply simple levels adjustments would quickly clip the ends. So it's a prime candidate for special handling.
The orignal, then 100% crops of 5 versions. Best to download these and load as layer stacks in Photoshop to toggle on and off for comparisons.