I'm using the Hoz&Shield 5 round extension. I have well over 2,000 rounds through it currently and it's flawless. There is user "fitting" that must be done to fit the new follower, but once completed correctly is flawless. Check out their website.
Lots of stages in PRS are 15 rounds, so a 2 round extension still requires a mag change.
Another option is to try the polymer Vudoo mag in your B14R. Then can get a 5 round extension for that as well. The Vudoo mag works in my setup, but after trying the Hoz &Shield extension, it was more cost effective to stay with Bergara mags.