Brittle and serpenstars, which are the same, are fine for this size tank.
IMO, there is NO reef safe star such as a Linckia that is suitable for this tank size.
Not the blue, not the orange...none. Most of these stars, even in significantly larger systems, will die of starvation within a year. A 29g is in general not suitable for one of these stars.
Ditto for the smaller Fromia star which is also not suitable.
That is not to say they will ALL die in this tank size, but MOST will die (quite frequently someone will say "I've kept one!" - but this is rare).
Brittle and serpenstars are fine, IMO, but they should be fed. The green is a known predator in the wild and probably any might have this potential in captivity as well. I have never had issues and I have about 11 brittlestars. The serpentstar sold here - that is black and white - is small and nice. The larger red one, IME, can be more aggressive, and definitely is less hardy than other species.
What are your specific water parameters and tank age? These are really critical to know before you purchase any type of star.