I am one of those people. I don't recommend UV's for most people. A quarantine tank is more effective and generally cheaper.
While I don't think UV's do much harm. I think the risk to plankton is overexaggerated, in my opinion, the bigger risk is the false sense of security they provide. "I don't need to quarantine. I have a UV!"
Even free, I would not run one and I can speak from personal experience on that point. I have gotten at least three units over the last couple of years. None of which I used. I have considered adding one to my freshwater outdoor pond though, but have not gotten a free or cheap one that can be used outside yet.