"erratic of" is a correct and usable phrase in written English.
It means behaving or acting in an unpredictable or inconsistent manner. Example: Throughout the trial, the defendant's testimony was erratic at best, making it difficult for the jury to determine the truth.
Valencia have been erratic of late but mostly the results have held, at least at home.
The Yankees are attempting to build Chamberlain's endurance in time for the postseason, but he has been erratic of late.
Dealers increasingly offer discounted satellite-radio packages.Messrs Karmazin and Stern have joined the smaller and more erratic of the two satellite-radio firms.
The most erratic of the somnambulists on this zigzag trail was the man often called the father of modern science, Galileo.
It is even more imperative now, with chaos swirling around the rotation, that Pérez, the more erratic of the two, supplies some semblance of steadiness during Martínez's absence.
While the genial Hugh does something in the City, the more waspish Sylvie, his wife, produces children and casts a sardonic eye over the family, but particularly over Hugh's sister, Isobel, or Izzie, who is the most erratic of the family, and blessed with a wild talent for self-invention.
It avoided drastic adjustments and assured continuity of the Programme in the face of erratic flows of Other Resources.
This season we get all of the erratic quality of the story with the sound structure of well-crafted television.
European decision-making during the crisis of the last few years also shares some of the erratic nature of Mexican policy under President López Portillo.
In his fictive movies he captures something of the erratic rhythms of real life under pressure.
As candidate for chancellor in 2002, he bungled his campaign, not least because of his erratic way of speaking (the verb "stoibering" has entered the German language).
