Lets say you deposit 20k in 3 separate instalments at the 5month rate, a total of 15months, this will give an interest of 678euro. One instalment of 20k at the 15month rate will give 660euro. Calculated on the interest calculator on their website.
Now, i know the 5month offer wont be around for long, but its basically the same deal... yes, you get your 226euro after 5months but you also have the hassle of re-investing again.