Easy enough to assemble, but once assembled it's too easy to get it apart. I found that the tension of the spring was enough to separate the pieces.
I used a heat-gun to adjust the shape of one half, so that it was held together much more tightly. It was correspondingly more difficult to assemble, but now that it's together, it's working.
The shape and fitment of the item is good, it works just fine as long as it stays assembled.