I have one word for this puzzle: remarkable! (Well, with all the synonyms of the word, there could be more than one in this case.)
"Cast U&U" turned into a favourite of mine only after seeing a picture of it when it was released in March 2014. Then, it was a period of desire to own this clever little puzzle. And at the end of October 2014 I got it in my collection from PuzzleMaster Canada. After that, it became even bigger favourite of mine.
The idea of "Cast U&U" is to separate the two Us. When looking (just looking) at the puzzle, one might think that moving the two pairs of nuts away from each other would make enough space for the two Us to be relocated and thus separated from each other. But when you have it in your hands, you can easily find that there will not be enough space to do that action. The six (to be honest, they are six - two pairs of three not separable) pieces are made so accurately that the solution is very, very precise and only that solution works and nothing else. No force, and - for those who count on it - no luck would help you in this one. You have to think what could be needed in order to separate the two pieces - that is, what the exact order of steps are necessary. Or, if you can't think that much - you have to look.
I really don't want to go into that much superlatives about the concept, the implementation and everything else about this puzzle. You have to own it to get it. I would just like to add that I solved it faster than I thought (I suspected a long time of torture), but still not that quick to just do it and leave it afterwards. I also think, on the contrary to other people's comments which I have read so far, that this puzzle is very pretty. I love the looks, the design, the grace and fineness it offers. For me, looking different than the rest of the Hanayama Cast puzzles makes this one outstanding.
Finally, if you are into puzzles for quite some time, you should try "Cast U&U". It would provide great experience and I hope you like at at least as that much as I do.