The G. Saglionis, called Giant Chin, is the most common of the genus. The Giant Chin, so named because the indentations between the areoles look something like a chin, is usually used as a potted specimen. In our 9b zone, it can take full sun and it's frost tolerant, so it's also a good landscape cactus.
Over time, it can become relatively large, over two feet tall and a foot wide. I saw one at a cactus show that was half that height, and the owner said he had acquired it over thirty years before. The flowers are urn shaped and close to the body of the cactus. They are a dirty white with just a tinge of pink.
I like this South American genus and have several of its species. However, this Gymno species is not my favorite. It grows so slowly that I don't notice a change from year to year. My cactus blooms only once a year, usually in mid-summer, and never has more than three flowers each season, unlike other Saglionis specimens that bloom repetitively over the summer. I don’t know why it performs this way. It's sort of like a green rock with spines.