I didn't see the link, but the general problem with many is that they have adds for, or are sponsored by, competitors. Hey, the mods (or at least speaking for myself) don't like it all the time, but unfortunately it is kind of the way we have to work it.
IMO -
NO on any Linckia in a 20g tank. Most will starve in 9-12 months. Until they are kept over a year, no one should claim any success. It is estimated that it takes 9-12 months for a healthy wild caught individual to starve to death.
Even if they do survive, they are CLEARLY in the minority. We know little about the dietary needs of these stars but there is NO DOUBT that success greatly increases with increasing amount of LR. But we know that they DO NOT feed on algae and detritus and VERY FEW will take to any spot feeding. They most likely graze on bacterial/algal films or the critters that feed on those things. And it takes time for them to regrow in an area covered by the star.
FWIW - Fromia may have an even more specialized diet. Smaller does not mean easier to keep.
IMO, please do not try. Will it definitely die? Not necessarily. Will it definitely live? No way. Is it responsible to try it knowing the success rate? IMO, no.
If this is a very well established flourishing reef tank, then there is the possibility that the small Linckia multiflora would work, but it is still not guaranteed...but it is a far better one to try if you are adamant about having one.