No, it's perfectly fine, saves you a good $60.
Usually its best to get the same kit/frequency with the same timings, but with generic modules running at 2133MHz it's fine to slot in another stick.
Tell us your full specs, the amount of RAM you currently have, and what speed it's running at.
Preferably brand would be good too, pull out the sticks with the system powered off and read off the side.
No, it's perfectly fine, saves you a good $60.
Usually its best to get the same kit/frequency with the same timings, but with generic modules running at 2133MHz it's fine to slot in another stick.