Multi Boxes have been around in QlikView for a long time. They can be a useful way of adding many selectors to the layout when there is little room for a lot of listboxes.
They can be presented either in the default, lateral mode, with the drop-down list across from the label, or in Grid Mode, with the drop-down list underneath the label.
I used Multi Boxes for many years and quite liked the Grid Mode style. However, there was a major problem. Unfortunately, the Grid Mode style is not supported in the AJAX ZFC web client.
Since Version 10 of QlikView, I have moved away from Multi Boxes and instead use a container control with listboxes. I believe that it is a much better way of accessing many fields in a small form factor.