Primal clients support this. On any profile screen, just select "add to my feeds" option. One of my favorite features.
Discussion
Does it load their relays?
Yes 🙌 It has many uses. Great feature.
It's what happens when you think source routing and multicast voluntary sharing that can also be filtered, and doesn't go to anyone you don't know.
Up to now, always there is a hub that all send to and who relays, the model originated with IRC. Smarter and smarter filters and your entire view is manipulated by a select few and their bayesian filters and now transformer matrix recognisers.
Welcome to the alternative path of the individual is central and there is filters but by design are opt in, and trustless.