I'm probably a bit late to chime in and I'm definately not the most knowledgable person but I bought one about 3 months ago as I had an outbreak of ich and didn't have a QT setup so didn't have many options
I will say it saved my tank from complete wipeout and one of my clownfish was on its last legs when I bought the UV
, it made pulled through!
Will also say I was having major algae outbreak on my substrate and in a week of it being on it cleared it completely.
I'm all for UV
steriliser's but understand that it's not the perfect ich solution, since then I've set up a QT for a back up!