I have used your method of plucking them out with good result in the past.
I also used harlequin shrimp to eradicate the asterina starfishes but feeding the harlequin shrimp afterward was a pain. So to save money and time, I sold the harlequin shrimp. I still have asterina starfish but very few here and there.
You probably want to continue plucking them out of the tank until their population is reduced drastically. Then, it’s just few here and there from time to time. Least for me.