Reference edition:

Commentum in Ciceronis rhetorica, ed. R. Jakobi, München Leipzig, 2002.

What we possess of the book stops at Inv. 1. 22, thanks to the defective nature of the archetype of the few manuscripts that carry the work. It was for long available only from the excerpts published by K. Halm in his Rhetores Latini Minores (1863), 596-606 (drawing on two local manuscripts). The whole text was first printed by J. Martin (Paderborn, 1927). Jakobi, in his Teubner text, was able to draw a stemma showing the relationship of six manuscripts, all dating to the eleventh or twelfth centuries, together with two descripti. The latter, together with two further manuscripts not registered in the stemma, he used as sources of conjecture. His commentary volume amasses a great deal more information on the fortuna of the book. Despite this accumulation of new material, the text remains insecure. For a number of suggestions see M.Winterbottom, ‘Grillius on Cicero’s De Inventione’, Classical Quarterly 54 (2004), 592-605; he judged the text as ‘not just corrupt but seriously interpolated’. 

Grillius was for L. Castiglioni ‘questo mediocre maestro’. His commentary is indeed neither elegant nor sophisticated. He naturally often illustrates his points from Cicero’s speeches, rather more of which he is acquainted with than we are. More surprisingly, he frequently adduces Sallust, Lucan and (most freely) Virgil (‘divinus poeta’). But those interested in understanding the De inventione will not find much to help them here.  [M. Winterbottom]