I also looked at the cactus-art site. On the pictures he showed is the first one a tlalocii, but when you click on the picture another plant shows up and this is a huitzilopochtli. The comment at the bottom is no helpfull either because it's about M. lenta. The second picture is no tlalocii either, but crucigera grandinosa. Cactus-art give another name: caespitosa. I wouldn't count on nurseries like cactus-art being a reference of correct names. The picture you showed from the BCSS Glasgow show is, and I repeat, M. huitzilopochtli.