LEGO is a registered and protected Trade Mark and is also copyrighted because of the special design. Unfortunately, unless you can claim the IPR and provide evidence that the fake UC100 is actually a copy of your specific product, you don't have much chance in a court process. Also, if you'd go to court you must be prepared to lose and that might cost you a lot of money in the end. I think LEGO has more money and a larger organization with corporate lawyers as support to deal with such things than you have. It can be difficult to fight these kind of people and businesses for a small company. If I were you, I'd buy one of these and would examine it carefully, to see if they just use the name "UC100" or the design is copied as well.
Yes, I don't have corporate lawyers support, except my niece's who is a layer, other than that we working with one other lawyer only when we make serious contracts or when we for example bought our warehouse etc., but he is not really specalised with this type of problem, I know that because we already had a similar case and had to work with another lawyer on that one.
So, I think the best I can do is talk to my niece first and see what advice she will give.
On the other hand I'm not optimistic about this as I'm a realistic thinking guy and for example I remember the case when a Gecko drive was copied by a chinese company about 10years ago where they clearly copied their design and however the original fake producer got stopped but that counterfreight drive as far as I know is still produced and sold. The counterfreit company can simply make a new e-bay account or new website or new company and can continue selling, so yea, I don't have illusions.
And I already saw the design of that controller and it is not a physical copy of our UC100, it is a different layout with different chips etc. and as mentioned with the DDUM controllers software which is a well known to be having problems controller...
What I'm the most sorry about is the customers who will actually buy this.