The piggyback tunes that plug into the rail pressure sensor trick the ecu into thinking the pressure is lower than it is. On some there is a dial adjustment, where some have found past 80% can cause codes or no increase in performance. That happens because the fooling can end up exceeding the rail pressure relief valve which is not a good idea to do more than a few times, as it wears out or something.

For the cost of those boxes, a glorified hack, better to just get a tune for a bit more which won't stress your injection pressures.