Hi Mike,
The value of the roller, and the large roller on the spring accentuated this effect, was the frizzen had substantial resistance to opening until the toe slid over the apex of the roller, and then any resistance to opening disappeared. The same degree of that effect is hard to reproduce on a lock without a roller. You can come close by making a feather spring with a hump at the end where the frizzen toe rides over it. When combined with a short throw flint cock powered by a strong mainspring, the roller frizzen purportedly increased the speed of the lock and ignition. Having built locks will all of those features, it is my sense that the large roller on the spring has stonger camming action than a small roller installed in the toe of the frizzen. Moreover, the large roller wears better and is less prone to locking up due to powder fouling. I believe those are the reasons the large roller dominated during the 19th century and the other system mostly disappeared. Both systems take about the same effort to make because the roller on the frizzen usually rode over a hump on the feather spring so for both methods you have to start with thicker spring material.
dave