At the risk of sounding repetitive, thats not the answer to the original question.
The fact remains, Cars fitted with these kits pose a risk to other road users and are illegal.
How you go about breaking the law or circumnavigating the MOT test requirements is up to you. But encouraging others is an entirely different matter.
The fact you are even recommending a way to do just that, just confirms that you know there is a problem with these kits, otherwise why would you need to make such a statement.
Misleading advertising and taking peoples money in the process, is a trading standards matter and a "Sale of goods Act 1979" offence.
Anyone caught and prosecuted for using these lights has a very substantial right of complaint and recourse at law against the supplier under that act.
The fact that a large number of these kits have been sold proves nothing, other than the odds of someone being prosecuted for selling them, are shortening all the time they continue to sell them.