The two of course are quite different. Mayfield to my eye was more instinctive in his play and reads, and had more boldness to him in the pocket. Nix is a bit less settled or comfortable in the pocket. The mentality of the QBs is something I value highly. To me Mayfield was much more of a McVay type QB in mentality and boldness. We saw that a bit, how they fed off each other in energy, in their brief time together.
In personality though Mayfield I always felt was a little childish, felt like he could use some maturity. But Nix strikes me as being extremely mature, he's a guy who I'd say is more ready to lead a team from that perspective at least.
So I do agree Nix has value to the Rams. It would be nice to have a QB with his talent sitting behind Stafford. What I don't like about him is his seeming dependence on the short passing game. Could he overcome that under McVay? Or would McVay wear him down like he did with Goff. I mean at some point a QB has to be who he is, if he wants to achieve the most he can, which means the offense has to either benefit him or be built around his strengths. So there is just a lot of projections and questions in my mind as it pertains to Nix.