I don't think that it does any indexing as such, and it works independent of Windows search.
But it's amazingly fast.
I just now had it search my D:\ drive which has over 400 gigabytes of stuff on it for any file with the .exe extension.
It searched the entire drive and found 849 files, and it took all of 28 seconds to do it.
As I said I've used it for years as my only way of searching for stuff on my computer.
I really couldn't get along without it, and I don't see any overhead at all on my computer.
And it's so easy to use, just right click on the location that you want to search, select AgentRansack, type in your search subject, and say go. It will remember what you typed in so you can work your way through multiple locations with out retyping.
The whole program installation, only takes 10.2 megabytes of disk space.
Just give it a try, it's free and it's never caused me any problems at all.
Just make sure you download it from Mythicsoft, the people who created it.
Because it's popular it gets stuck on a lot of sites that want to add stuff on to the download.
I've never used the pro version, I've always just installed the free version and it's done everything that I need.