If you look at Fielding Bible stats Jeffers is basically average defensively
Fielding Bible
His arm cost the team 1 run over the course of the season. That's it. He rated higher than both Narvaez and Barnhart. The total runs saved for Arm range from Realmuto (+9) to Kevin Plawecki (-5), This is the easiest thing to measure for catcher defense BTW. You either let the runner advance or you didn't.
Looking over the free agent catchers Christian Vazquez is the cream of the crop defensively (11 runs saved overall). Narvaez (2), Sanchez (1), Contreras (-1), and Barnhart (-8) all rate lower than Jeffers.
Vazquez has a .682 career OPS vs RHP and .731 vs LHP. Jeffers is .617 vs RHP and .794 vs LHP. They complement each other pretty well. Put them together and you have a .730 OPS catcher who is a plus defender.