Ive used this policy twice.
The first time, my primary flt canceled, so i called scheds. They were short fo's so they immediately ps'd me on the next flt.
The second time, i did not get on my primary flt, so i called sheds. The secondary flt was oversold, the scheduler said they had coverage so it was up to me whether i got to work or not. They said to let them know if i wasnt going to make it either before or after trying the secondary flt....which was a roll of the dice for me cause my secondary was due to arrive very close to report time. Luckily i made it on the flight and all was good. Basically, i think its a fair policy, if you abide by it to the letter, you will not get in hot water, but, you may lose the value of your trip. If you absolutely cant afford to lose the value of your trip then you just have to give yourself more options.