The novak smart stop will protect teh lipo since it interrupts power at the lvc. With an alarm, you run risk of not noticing the flashing light or hearing the alarm. The alarms are far easier to install and transfer from lipo to lipo easily. The Smart stop is pretty much permanent and also more expensive.

If you're running by yourself, alarm might be an alternative, but if you're in a group or racing, alarm may not be noticed. Smart stop is less risky and would be my recommendation.

Thats the way I went when I started running lipo on my Emaxx - I installed a Smart stop.