I had one years ago (probably 15 years) when I went to Egypt, because skimpy swimsuits or bikinis were frowned upon.I didn't get much of a tan TBH, mainly covered up on museum visits or fastened to the toilet 
.
But I didn't have white strap / swimsuit marks.
Are they still available? I've got a holiday booked in August and I'd rather wear a one piece than a bikini.
TIA