nothing worse than the plastic hex coming off with the wheel & the small pin falling out never to be found again.
Plastic ones also can deform , making wheel hard to fit on/take off.

I bought some 3racing locking hex's a while back. I have yet to find ANY rc car that they actually will clamp down on.
Luckily I some some spare locking hex's I can use on the mini
(Come on Tamiya, would only have cost beggr all to include them)