The beep sounds exactly 30 seconds. Personally, I see that as an advantage, because he does not bother forever if you can not turn it off straight (it is for example in the shower). But others could it thus "miss".
A big advantage is that in the Timer Micro cells (AAA batery) are used and no button cells.
If you pressed the button for the minutes and the seconds holding to adjust the countdown time, the timer counts quickly to confirm until the required time high without any minute / second with a beep. This is very pleasant if you want to set, say, 45 min.. Individual key presses are confirmed with one beep.
[UPDATE 10/2013] In the meantime I bought another timer, and this confirmed with the button pressed every minute / second with a beep. That annoys me so much that I pull a star. [/ Update]
The only feature I miss is a memory for two to three hours. For recurring processes, such as baking bread every morning at the same time, this would be a useful feature. Although it stores the last value what a but does not work, if you then for example used (with a different time) and the next morning must set the time rolls him for a cake. This was aware before buying leads and in my eyes not to deductions in the rating. Want it however mentioned for completeness.