Edit: ignore me, I apparently cannot read
Since when do insurance companies approve car mods? And what does that have to do with something being legal?
The only federal legal restrictions are on emissions equipment and safety equipment like seat belts and airbags. Some states have additional laws like tint limits and exhaust sound limits.
And any mods have to be reported to your insurer in the UK, even if it's just changing rims or putting on non-standard size tyres - failing to do so might get your claim denied if you ever file one.
Not that they wouldn't try.
Same as the whole "warranty void if seal is broken" nonsense.
I think since the default is for something to be "legal" until it is made "illegal" it makes the phrase "already legal" an uncommon one.
Probably illegal to drive this on any public road, however on his own property/private roads he is having a blast.
There's obviously legal nuance involving speed, safety, etc. But propagating a cultural assumption of "doing something weird must be illegal" is frightening.
Not with Tesla recording remotely what "owners" do with their cars.
I'd want a lot more roll cage than he has on there.