I shift HARD All the time. This was the second Shifter Kit bike made, put on a well ridden mid 80's Diamond Back with a lot of wear - the chain had some bent plates to start. I routinely experimented with it for 1.5 years (so far!) - purposely dumping the chain. Proves that chain breakage won't be a problem if you start with a good chain. The only thing that happened is the bike just was gliding with chain off so no real worries about going down. This is because of two freewheels. I didn't even know I had a busted plate until after I put the chain on second time and it kept jumping.