This incident is mysterious. Zipporah immediately circumcising her son suggests she and Moses had previously discussed it and decided it was unnecessary. Why would having an uncircumcised son make God want to kill the rescuer he had prepared and called?
It would seem strange for Moses to arrive in Egypt claiming to represent the God of the Israelites' ancestors, but would not do what God commanded them (Genesis 17:10). This might cause the people to be less willing to follow God exclusively.