Lost Dogs are similar to the blemished 7thfloor units. They can have a nick or a scratch, but it doesn't affect how the units work. I think Dave doesn't put them on his website as a favor to us FC users, think of it as a privilege you know about them at all.
I've never used either but from what I gather there are a lot of differences between both products, especially from a users point of view. I'm going through the entire UD thread as we speak and there have been a few comparisons between the UD and the CRZ already (I'm at page 34 atm).
Most important differences I noticed so far (from reviews of people who had or have both vapes) is that the UD runs hotter, has better airflow & suction, & a bigger bowl which is also changeable in size by moving the screen. Then there is of course the difference in materials used in the airpath, and a very big difference for me personally: the UD ships worldwide.
Last edit: I think if conserving and low-tolerance are keywords to you a CRZ would probably suit you best, but if you prefer a heavier hitter a UD seems the more satisfying one here.