[Freon]

We're digressing, but... I've always been wary of piggybacks for the issues outlined above, and I'm amazed the JB seemingly works so well.

There's only so much you can do simply intercepting and adjusting a small handful of signals even with the most advanced processing and engineering in your blackbox piggyback device. It's ignorant of a lot of information since it simply doesn't intercept the signals, and unable to affect as much for the same reason. It's simply limited in terms of I/O, and that's definitely a concern with something that comes from the factory already highly optimized. The factory ECUs that come with your car have tens or hundreds of million (cumulatively over the years and iterations) in R&D and far more ability to tailor operation according to a wider set of variables.

The biggest detractors are to producing the first viable product. They can be nearly impossibly to actually hack into to enable third party reflashing, and often the tuning tables are very hard to tweak by hand (I suspect these days they're tuned by computers or complex math, and dozens or hundreds of hours on engine dynos, especially things like closed loop control PID values and whatnot, but it's not insurmountable, go hit Youtube for PID control loop tuning and enjoy the wall of calculus, things like root locus controller design). But that is typically the issue of the company who first hacks it (i.e. Cobb, Dinan, GIAC, APR, etc) and produces a tune.