I've used Chikoo for several days and decided to purchase after my initial testing.
What I like is that it's fast, bloat-free and works well with files/folders on external as well as internal drives.
Check out the videos on their website - I literally understood how to use it in 5 minutes by watching the first few videos.
I've used Devonthink and EagleFiler before and while they are more powerful for my purposes I found they are also quite resource intensive and complex to maintain over time.
Do note that instead of indexing file content Chikoo looks at Name, Type, File Name, and Path, as well as any custom text attributes you may add yourself.
To me this is an advantage as it works fast and doesn't change the location of my current files (I tested on my largest database of 700,000 project files and it pulled up a search in 3-5 seconds).
By using Spotlight, Chikoo and Fresh for Mac I now have my dream system for pulling up any file I need quickly. Fresh handles all my recent files, Spotlight anything recent that Fresh doesn't and Chikoo helps me find everything else.
The developer has been very responsive to my questions and suggestions so I suggest you at least check it out to see if it works for your workflow.