Great module.

I just think that displaying the checkboxes horisontally is a bit counterintuitive, would be much better if the order of display was vertical columns. I mean top to bottom, instead of left to right.

To make it just a single column I can use CSS

.taxonomy_browser_checkboxes .form-item label.option {
  clear: both;
}

But because I have 500 items, it's good to have 5 columns. I guess CSS is not sufficient for that?