I've got a K1. Works great, use it all the time to print stuff. Only physical modification I've made to it was a printed dryer hose hookup that mounts to the back vent fan so I can pump fumes outside.
I rooted it to install Mainsail directly onto the printer's onboard computer and I use OrcaSlicer so you won't be stuck with the Creality slicer app if you don't like it.
I haven't done anything maintenance wise yet except keeping the rails and screws lubed.
Massive step up from my Ender 3 Pro. Only gripe I have is the filament run-out sensor sucks because it won't stop your print if the filament breaks in the Bowden tube (but there's a simple mod for the stock extruder to put a run-out sensor directly inside it to solve that problem).
If you can afford the cost/space and want to print big stuff, get the K1 Max instead.