Ok so I've seen some of the XD Compacts with an 'XML' light and a few with an 'X2' light mounted on them. What's the difference? I believe they are made by the same company and they look very much alike. I'm curious because I plan on buying one of them soon and most websites have prices that are close to one another, even between these two models. Is one of them better or brighter or something like that?