In my phd work I was heavily involved in hippocampal segmentation, and I can say with confidence that FSL FIRST is not a state-of-the-art segmentation method. It belongs to an earlier generation of segmentation methods with poorer reliability, which have contributed to a lot of contradictory results in my field of hippocampal development.
I would not use it in my research.
https://www.researchgate.net/publication/273940329_Assessing...
https://www.researchgate.net/publication/260915135_Volume_of...
https://www.researchgate.net/publication/274252280_Developme...
[edit] I had meant to point a link to my chapter on hippocampal development. https://www.researchgate.net/publication/314194708_Hippocamp...