Here is a snippet from the review:
"... Our goal was to determine whether the Jaked also works in minioren and juniors on the basis of what we have seen is the answer an unqualified yes. The non-water permeable material which is made Jaked also the youngest swimmer little higher on the water so they are quickly coming. The effect seems to be greatest in butterfly and breaststroke, because the attitude in passing (somewhat diagonally relative to horizontal backstroke and free stroke) there seems to ensure that there is more upward force is created.
When asked how much it saves is no clear answer, which differs greatly per swimmer. But our expectation is that the breaststroke and butterfly 1 to 2 seconds per 50m could, with the effect sometimes can be greater in the slightly less talented swimmers. This group is often naturally deeper in the water and would therefore have benefited more from the uplift of the Jaked. ..."
Here is the link to the English version: [Link]