Coming back to this, just looked into EU regulations and it's clear these are not outright prohibited

No law expert either but the pointy figurines people put on the hub front in the 70s? They are illegal; not specifically but by endangering all the other participants on the street. Bet wheel spikes fall under the same rules.

Btw, this is something i observed recently: US tends to make rules reactively and case-specific, which is why it needs to also define wrong-doing or not specifically ("don't dry your hamster in the microwave" warning label). While europe countries try to abstract general rules, just like in this case. I think the second approach works better for a healthy society.