let data = Array.from(document.querySelectorAll('.reviews__row .reviews__card')),
    step = 3,
    item = 0;

data.slice(step).forEach(e => e.style.display = 'none');
item += step;

document.querySelector('.reviews__button').addEventListener('click', function(e){
  let tmp = data.slice(item, item + step);
  tmp.forEach(e => e.style.display = 'flex');
  item += step;
  
  if(tmp.length < 3)
    this.remove();
});