It was tested on a lake, with multiple smartphones over several days.
The charging power it delivers is acceptable.
The only drawback: the cable that leads from his pocket going down behind a "hole" inside - I would have liked more of a "fixed" box, in which you plug in the charging cable / terminal, because with improper use (eg a drawing. the cable of the cell) possibly can break the cable - but then I have not tried.
Is it possible - for the price - highly recommend for sunny weather and a charging opportunity when times no socket is ready.