Its not HARD, its just hardER. The SMC kit is pretty much a drop in, connect a couple wires (1 plug, ground and power) tap for boost signal, install the nozzle and go. There is a lot more fo the other kits.
I am by no means bashing the other kits out there, as many of them have some REALLY nice features, but for 99% of people, the SMC kit does everything they will ever need.