Digging around in the learned literature of the late nineteenth century I find a gem, a review by A. Robertson of Batiffol’s Syntagma doctrinae in The Classical Review 6 (8) (1892), 351-354. Far beyond its value as a review is the discussion of earlier work on the Syntagma and the Fides patrum, and in particular a trenchant discussion of Revillout’s theories about the derivation of these documents, alongside the Gnomai, from the Council of Alexandria.
There are also some interesting reflections on the credal form found in the Syntagma, and on the value of the document with regard to the text of the Didache.
Those without easy access to an academic library can find this with relative ease on archive.org.