How predictably will RNA polymerase not transcribe repetitive sequences?
I don't think repetitive sequences are intrinsically problematic to an E coli. Bacteria also deal with things like polyadenylation. Basically, you have nothing to lose from trying -- E coli is one of the more robust expression platforms, and it's difficult to predict whether the sequence will fold into some tertiary structure (which can easily impede translation.)

So I think the predictability should be set at the baseline for E coli RNA polymerase error rate, which is about $10^{-5}$.