I tried the genuine "SmarteX PEX Pipe Disconnect Kit" and, frankly, it was absolute RUBBISH - just too damn small to get any sort of grip, and you need LOTS of pressure to disconnect a PEX pipe.
My version actually works, without having to resort to pliers/spanners/swearing so you can apply enough force to disconnect the pipe from it's fitting.
You can easily see the difference/problem in the picture - original in Grey, my working verssion in Black - any plastic should work, I used PLA (only because it was sitting in my #2 printer),
Another 21st century design - "LOOKS PRETTY - DOESN'T WORK"
FYI - although Smartex's disconnectors are garbage - their actual Push-Fit Pipe connectors work really well