I also have star polyps and they grow fast that’s why they are also referred to as grass coral or carpet coral because they grow quickly and end up looking like a carpet of grass
I personally love the look of green star polyps, especially in a high flow area. They "wave" in the flow. But as others have said, they do tend to spread fast and will grow over other corals in their way, so do be careful of placement!
I love them too but like I said they do grow at a very quick pace and just make sure you put in on a rock that’s not touching other rocks so it can’t spread to other rocks and then go to other corals