Definitely agree with the above.
IMO, and as an aside there are very few animals in our tanks that meet the hard core definition of reef safe (meaning they would only ever eat algae I guess). Crabs of all sorts, shrimp, urchins etc are all commonly kept in our tanks as "reef safe" when in fact they are quite omnivorous. Lots of chances we take without thinking about it, that probably pose a more realistic threat.
As far as the star goes, it has far more worries about survival. It may eat sponges and tunicates...may not...maybe only some...and probably you would not see much of a difference because the tank often does not sustain many of these types of animals to begin with.
We know that Linckia do not eat:
-detritus
-algae in the sense of nuissance or macro algae
-overall meaty things
We suspect they eat:
-biofilms and the microbial life associated with it
-perhaps certain encrusting animals like bryozoans
-possibly certain types of sponges, tunicates and the like, as mentioned.
We know that Linckia can take an extraordinary amount of time to starve, over a year, and that there are few if any signs of trouble. 18 months is the "success" mark. Many claim success long before this..long before they should.
They are, in my book, an animal for the "ban" list.
Other things to consider: If your LFS does not acclimate, or keep their specific gravity around the 1.025 -1.026 mark, then I wouldn't consider them. As mentioned, if your tank has less than a minimum (absolute minimum) of 150lbs of LR, it is also a concern. If the tank is less than 6 months old it is a flag. Acclimation time is also critical.