It depends on how that auxiliary "safety lever" is mounted to the main brake body. The cheap ones had a part that fit between the main brake lever and brake body thereby greatly reducing the amount that the main brake lever could travel. That reduced the amount of braking possible with the main brake lever. Additionally many of those "safety levers" were quite flexible and thus had poor braking.

Some of the safety levers were better designed and were fitted directly to the main brake lever and were quite rigid.

I don't think that "safety levers" are all that safe and I'd remove them. Interrupter levers with aero main brake levers is a much more positive braking system.

If a person rides on the top of the handlebar a lot then the stud sticking out from the side of a safety lever pivot can be modofied to mount either a downtube shift lever or a stem mount shift lever.




Cheers