That may be the case in Germany, but in the UK, unless something is obviously unsafe, I don't think this would be the case. For reference, a certain culture of ridiculous body kits and spoilers would be in a lot more trouble, as I'm pretty sure that most of them do not undergo any testing, and that doesn't account for "home-made" versions.
If that were the case, how would people ever transport anything on a roof rack? That is effectively all the project is doing (somewhat pointlessly in my opinion, but each to their own). That's not to say that they won't get stopped for some kind of lack of photography permit, but not for any of the reasons you have outlined.