It's very easy to control the problems (and they're not that big issues, seeing as way more complex and far-fetched stuff has been made). I'd imagine that the clock either blocks/muffles the sound when it's not alarm time, or the koyukkuris are simply too terrified to make noises and spend the time constantly begging to be spared... then electric shocks galore. The latter seems more likely and also more appealing. A constant background of yukkuri suffering and begging as well as authentic terrified koyukkuri screaming might be a very nice thing to wake up to, for some people. Or even to go to sleep to...