I will badmouth Netjets as much as anyone alive.
That being said, when it comes to limiting or helping with getting a job at the majors, it cuts both ways if you are someone looking to come to Netjets as a stepping stone:
NJA hurts you in that non-121 is looked down upon.
NJA hurts you in that you'll not get any PIC time.
NJA hurts you in that the type rating you get does nothing to enhance your resume.
NJA hurts you in that you log less time here than at a regional/national airline.
NJA helps you in that you will have diverse flight experience.
NJA helps you in that you (should) get excellent customer service experience.