I cannot confirm 100% because the other demos for BurnEngine do not have these options built out, but in BE v1.1.5:

BurnEngine > Control Panel > Theme Settings > Store > Product Page > Option Styles

When setting a checkbox to be displayed as a button, it does not appear to be working correctly. No button is displayed, only a miniature box is shown with no label.

I think this may be caused by the following CSS:
.options .tb_style_2 .checkbox > label span, .options .tb_style_2 .radio > label span, .options .tb_style_2 .checkbox.image > label div, .options .tb_style_2 .checkbox > label input[type=checkbox], .options .tb_style_2 .radio > label input[type=radio] {display:none;}

When it should be:

.options .tb_style_2 .checkbox > label span, .options .tb_style_2 .radio > label span {display: inline;}

.options .tb_style_2 .checkbox.image > label div, .options .tb_style_2 .checkbox > label input[type=checkbox], .options .tb_style_2 .radio > label input[type=radio] {display:none;}

Not a huge deal as this can be fixed by adding custom CSS, but worth pointing out because it doesn’t seem that the custom settings dimensions are working either.