Dear Jeffery: I recently purchased a set of Riser Mini-Cups and, as a collector and performer, I am very pleased with my purchase. The cups are expertly crafted, heavy for their diminutive size and have that special squatty/thermos cup look that is so desirable. They can handle a size ball which many mini-cups cant do so well.
You may want to check out James Riser's web site to get a closer look. Riser's web site is also a lot of fun to surf because it contains quite a bit of information about a variety of current and historic cups. The plentiful color photographs are also interesting.
Finally, I found Mr. Riser to be good to work with during the buying process. He answered all of my questions promptly and was good about getting the cups to me in short order. All in all, a pleasure to deal with and a great product that is well worth the investment (in my humble opinion).
Here is the link: http://www.jamesriser.com/Magic/JamesRiserMagic.html
I have not seen the El Duco Mini-cups so I can't comment, but I have seen the regular size and I thought they were quite nice too. Hope that helps. Regards, Robert :)