Does Fileseek build an index? That looks like a primary difference, that Everything's index database can become old if you don't leave it running (minimized to taskbar tray), or be waking up drives to scan for changes when you load it if not kept running in the background, but then when you search for something it is lightning fast to not have to search all volumes again, literally only takes milliseconds to display the results and I'm talking about results from over 20 volumes, over a network, removable devices, memory cards, DVDs, flash drives, etc. that aren't even plugged in.
I do have Everything on a system that it has ran on for a while, but I can't remember the syntax for certain things like searching for *all* duplicates. I mean I know where the file is that I put a list of these search modifiers in but I never did memorize them.
Everything did have some sort of bug that effected my use, something about losing the results on network shares and then rebuilding the index every few minutes regardless of what that interval was set to be in the program, but I reported that and they came out with a fixed version, maybe a year and a half ago.