I haven't used those, but saw something very similar just last week on the Kinsman Garden Company's website. Their version is made out of a flexible silicon rubber and according to their website can hold bamboo, metal, plastic or even tree or branch trimmings. Because it stretches, it is supposed to be able to hold a stake with a 1/4 inch up to a 1 inch diameter. They sell a package of 6 for $7.95. Has anyone ever used this type?

Here is a link that might be useful: Cane Connectors at Kinsman Garden Company