There is a ton of legislation regarding them and I believe it varies by state...though don't hold me to it. There are companies that sell the shoots, like you pictured, but I'm unsure how they are able to do so besides that being the only stage of life one is able to sell them in.
Besides that, they are a poor means of nutrient export and not worth the time and effort.
Some keep them, but they are a pain to successfully keep as they need daily spritzing of fresh water to hydrate and keep salt creep away. I wasn't able to keep them alive. In the end algae is much easier and better exporter of nutrients.