This jins is fairly rare in mid-20th century Arabic music, and more-or-less nonexistent in contemporary music (except among some educated reciters of Qur'an, and of course musicians who play older repertory). However, it was tremendously common in the early 20th century. Similar in its relation to Saba as Secondary Rast is to Rast--it has a nearly (but not completely) identical intervallic structure--Secondary Saba emphasizes its third scale degree rather than its first, and hence can feel like a form of Hijaz with different notes underneath. As is the case with Jins Secondary Rast, the use of two numbers in identifying the Jins (i.e. "Jins 2nd Saba 3/5") refers to the traditionally assigned tonic (3), which is the starting point of the Jins, intervallically speaking, but which isn't a true tonic - the true tonic, the note of melodic resolution (and the common tone in modulation from other ajnas), is the second number in the pair (5).
Compare these examples of conventional Saba; first, as the root jins of Maqam Saba in the Umm Kulthum song "Huwa Sahih il-Hawa Ghallab":
As a secondary jins on the 5th scale degree of Maqam Rast in Aruh Li Meen (#40):
Similarly, in Ghannili Shwayya:
And similarly in the Nahawand/Nakriz context, in Gameel Gamaal:
Now, hear the difference in tonic emphasis in these passages--where the shared "common tone" with adjacent ajnas is its third note, rather than its first. First, descending from the octave in Maqam Rast--the most well-known contemporary example, from "Ya Maal ish-Sham" (#38):
From a Salih Abdel-Hayy Dawr "Ijma3 Shufna" (as the opening Jins):
From Abul-3ila Mohamed (first decade of 20th c., one of Umm Kulthum's early teachers and composers), Mawwal Rast "Fein Ya Gameel Wa3dak" (#10, #13 & #15):
similar to the usage in Rast, descending from the octave to the 6th Scale degree; Muwashshah "Ayqadha-l-hubbu Fu'aadi" (#13 & #15)
this time a different usage, descending from the fifth scale degree (the shared common tonic with Jins Ajam 1 & Jins Hijaz 5) to the third scale degree--from the Umm Kulthum song "Lissa Fakir":
with the same relationship to Ajam as the previous example (between Jins Ajam's 3rd and 5th Scale degrees), but descending from 8 to 6 relative to the root tonic of Maqam Zanjaran--in the Muwashshah "Aya Daraha bil-Haqq" (#15):
It is worth noting, however, that what i refer to as "Secondary Saba" is actually the primary form of Saba within the Turkish Makam tradition. Whereas "Secondary Saba," tonicizing its third scale degree, never occurs as a primary root/final jins in the Arabic tradition, it is the main form of Saba still practiced in Turkey. Greek forms of Saba sometimes follow the Turkish model, and sometimes the Arabic model. For these reasons, it is especially useful to distinguish these two forms of Saba, each of which has particular melodic consequences. Maqam Saba in the classical urban tradition of the Arab world does draw from the melodic vocabulary of both forms of Saba--whereas folk musics from Egypt, Lebanon, and Syria exclusively use the "Arabic" Saba, frequently without ascending to any other secondary ajnas.