Originally Posted by
Arrowana
Aside from having extra flex to reduce braking power, safety levers also make for a less ergonomic lever at the hoods. From a functional and ergonomic standpoint the best choice is swapping to aero levers and interrupter levers, or swapping to a different type of handlebar entirely if the rider won't ever be riding in the drops or on the hoods.
If the rider cares more about the bike being as close to all original as possible, or as period correct as possible, then you might as well keep the safety levers if they want them. As long as they aren't conflicting with the handlebar, they usually still work ok enough if you aren't trying to use them to stop in the rain with steel rims.
As clever as interrupter levers are, I find that most feature a poor shaping of the lever, and all of them lacking in leverage (as compared to safety levers).
Since the cable housing stops on the interrupter lever do not swivel like on all other brake levers (either the cable head or the housing stop itself actually swiveling), these levers are purposely designed to effect
greater cable travel over a smaller angular movement of the lever.
As a result of this design compromise, the leverage is poor, made worse by their (usually) poor lever shape and seemingly shorter lever length).
Shimano, for their part, has recently offered
hydraulic interrupter levers as optional on their GRX-series of gravel bike components, having no such compromise.
But neither Shimano or SRAM has offered a cable-operated interrupter lever, which I think would have been a good target for their engineers to go after, bringing their powers of innovative re-design to a part that needs improvement.
I think that a
swiveling housing-stop barrel could be incorporated into an interrupter lever though, allowing a greater leverage ratio matching the main brake lever.