Although the vibrate mode is short, it does continue to vibrate intermittently until you acknowledge the timer is up by pressing “ok”.
I agree that the ringer tone is hardly audible and no option exists to affect it.
Still, I think that in vibrate only mode this is a very useful program. I used it last night while studying for an exam and the count down feature works flawlessly. I think this would've come in handy for LSAT preparation. You can't hear the vibration on a train, but you can certainly hear it in a library and its not loud enough to bother other library visitors.
Don’t use it to time the food in your oven while you play Halo though; that won’t work out to your advantage.