They are well made metal tubes, I really can´t go in much detail since the product is not very complex. I think, for most people who don´t professionally play music or players who aren´t only focused on slide guitar, this is excellent. If you are just going to use them from time to time or for some songs it´s a great thing to have, really does add something different to your playing.
If I have to get picky on my personal experience, I would say the large one is a little bit too large for my middle finger and the little one a bit to short to cover all the strings. Also, they feel a bit broad, so unless your fingers are thick, the slider might wiggle in your finger. But again, I guess it depends on your finger width. I can say that the large one is a bit longer than the width of the neck board on most of my guitars, maybe it can help you visualize it better.