I confess that I find the range of topaz plugins and apparent overlap of features to be a bit confusing.
I can understand that, but it's partly due to their business model; purchase once, free upgrades for life. That means that they need to keep producing new plugins to attract new customers.
Fortunately, with the new plugins also comes new functionality, and some have pretty good functionality or real improvements over previous versions, although some plugins have a bit of an Instagram type of functionality (some even have a 'I feel lucky' kind of Random settings button) if one only uses the presets.
But the underlying technology is quite good, one just needs to decide ahead of time what the goal is that one needs to work towards, and which tool is best for that.
Sofar, 'Clarity' does magic for how (local) Contrast is rendered, and 'Detail' does wonders on structural detail. Both are very important for rendering images that have a tangible feeling to them. Sharpening is always important, although their 'Infocus' plugin could use some upgrades in functionality. Those are the plugins I'd concentrate one.
The 'Denoise' plugin does a good job on most images, as long as one doesn't try to remove
all noise from high ISO shots. Besides, a bit of residual noise rarely hurts. The Remask plugin/application is quite good as well for masking/extracting subjects/targeted processing.
The recent 'Texture Effects' is very capable for adding effects, textures, borders, etc., if that's what one wishes to do. It also shows the latest insights in Topaz Labs' approach to a user interface for multi-layered effects, quite effective and it reduces clutter in the interface (which is hard with a gazillion controls). They've also added the possibility to use one's own textures/borders/grunge/light-leaks/what-have-you effects, or share settings with an on-line community. That should help their revenue stream I'd think, but it's also very effective productivity tool if such effects are needed on a regular basis (and much easier than Photoshop for most users).
Even their 'Impression' plugin/application does a decent job in mimicking painted/sketched versions of photographs, and it's very fast compared to alternatives like Corel Painter (although that allows even more control for artists with real drawing skills). Impression could use some more user control over the brush types and application of them, but there are lots to choose from already.
But they also have specialized plugins for specialized tasks (e.g. DeJPEG to improve JPEG input before post-processing it further), not too much functionality overlap with other plugins there.
Just make sure you know what you want to achieve before choosing the tools. The tools are merely a way to achieve the artistic intent with which it all starts, and do it in an effective/productive manner.
Cheers,
Bart