隻有傻瓜才購買這種可在購買後一個月 can be called away.

You at least need 6 months guaranteed rates.  Some callables the call schedules are once every 3 months AFTER the first 6 months.  Those even at 0.1 - 0.2% lower rates, still far better than callable that can be called just one month after purchase.   The worst scenario is,  you have a ONE MONTH instrument which is 5.8% APY versus other instruments that might be 4.8%+.   The difference is 1% for a Whole year.

So for a principal of $10K, the difference in the interest earning is $10000 x 1% /12 = $8.33 per month.

Who cares for that peanut extra?