I've tried Karabiner Elements for quite some time. Because I came from Windows and wanted to swap some keys around (command/control and some shortcuts).
It seems to me that it made input lag sometimes worse and also just ate input more often that when I uninstalled it. I mean this piece of shit i9 2019 MBP does that sometimes anyway when under high load, but happens more often with Karabiner installed.
I have been using Karabiner Elements for nearly a decade and have never noticed this. To me, it's indispensable (I remap Caps Lock to both CTRL and ESC depending on whether I hold or tap) and it's the very first thing I install when I get a new Mac.
There were some hiccups around the time of 10.12, but the developer resolved all the ones that I saw.
I have control and command swapped in system preferences and the only other key combo I use is the CMD+Tab and Ctrl+Tab[1]. I have no issues this way. I will say system preferences is where I put all other key combos linked to AppleScripts.
It seems to me that it made input lag sometimes worse and also just ate input more often that when I uninstalled it. I mean this piece of shit i9 2019 MBP does that sometimes anyway when under high load, but happens more often with Karabiner installed.