If you read the thread I linked, I believe there was a post from someone with rearsets saying he put the safety spring on as well...though not sure if these were the Madass kit. Basically, you need to check what can happen if the cable were to fail...does the lever flop down to the road surface (or close when leaned over in a turn etc)? If so, the spring will help. Others have used rubber strap (inner tube) to act as an alternative failsafe device. I'm of the belief a hard stop could/should be made on the lever to prevent the issue.