Kinshasa is good place to live and especially Gombe. I grew up there, the place is safe.
Security mainly depends on your actions and choice. For instance late night walks in isolated places, making cash visible. You'll especially need to be aware of the pockets of insecurity in the city and especially where to go after 6pm.
Just make sure you have a congolese friend whom you can trust to advise you on some of your actions and steps in Kinshasa and you'll surely have a good time.