Whether an aftermarket electronic computer unit is easier to repair or not is a very subjective – as even the term “aftermarket electronic control unit” is a relative term. In most cases, if you are trying to increase the power output of your car, you will probably be hacking around with the unit that specifically controls not only the advance and retard of your injection system, but also will inject more fuel into the fuel-air mix at the same time. Usually this means that unless you have a docketed device, you will have to be pretty good with a small soldering iron. This is because you will be soldering new memory instructions into place with surface mount memory which is actually small and somewhat hard to work with, especially if you have never used a soldering iron before.
For more info, see Choosing the Right Aftermarket ECU