Peter,
When you buy Topaz you get a year of upgrades included and they are fairly regularly upgrading their products. After the year they give discount pricing on upgrades and of course your software continues to work if you don't upgrade.
Sometimes the results get funky but in my experience I find it works more often than not and sometimes it is almost scary in what it does.
For example this is a 400% zoom in:
I have the pair of Gigapixel and Sharpen AI and typically try both on an image I want to process. Sometimes the scaling in Gigapixel does a better job of sharpening or I scale in Gigapixel and then use Sharpen.
The auto setting can work but I often try the different modes to see what happens. I don't use it as my general sharpener but use it when trying to rescue an image that isn't as sharp as what I want. One other thing it does, that is fairly hidden, is the ability to selectively sharpen through masking. You can also have the software analyze the contents of an image and sharpen (or not) specific objects it finds within. That can be really handy when you are pushing the sharpening for one area and want to avoid artifacts elsewhere.
As an example...
Original image Nikon 500mm F4P with TC-301 on A7RII, I missed focus slightly
Topaz Sharpening over the whole frame in Focus mode. Some artifacts in the water.
Topaz Sharpen AI (set to focus mode), on this I had it find objects and it identified a bird in the picture and masked it so only the bird was sharpened.
Hope this helps,
Shawn