So if I recall, someone here had a TIA with On-X at the lower range. My cardiologist nurse said same thing when we discussed lowering my INR from 3.0 to 2.5 that they knew of a patient that had a stroke at the recommended 1.5 - 2.0 range. My goal is to target around 2.5. My latest INR is 2.6 on CoagSense which tends to run accurately to a tad low.I don't know much about On-X, but before the FDA approved it, I'm sure that it went through a LOT of testing.
If mine was On-X instead of St. Jude, I'd still be more comfortable keeping my INR around 2.5 than in the sub-2 that On-X says is safe. In this case, with 2.5 also being at the bottom of the range for St. Jude valves, the INR management may be similar - so perhaps the big difference would be that the On-X is quieter than the St. Jude.
We'll probably know better about any failure rates with On-X a decade or so from now. (I'm not sure that I'll be here that long, but, if not, my exit most likely will be unrelated to the St. Jude valve (aside, I guess, from really stupid INR management).