The real kicker is that, more often than not, imitations parts are of inferior quality and performance. Imitation parts may be cheaper up front, but they could cost you a lot more in the long run.
For starters, imitation parts typically don't last as long as genuine GM parts. Unlike genuine GM Parts, imitation parts typically aren't built according to your GM vehicle's specifications, leading to possible mechanical problems and system breakdowns.
Imitation parts are often produced using substandard materials that don't hold up or perform like genuine GM Parts.