We're glad you like it! The Banner / Slider Solution will adapt its height automatically based on the content you add to each item. If you want to show images without content, you could always paste the following into the source view of the "Slide Content" editor on your item edit page:
<div style="height: 400px;">
<!-- don't delete this div, editor -->
The HTML comment saying "don't delete this div" in the code block above is there to prevent CKEditor from deleting the div because it thinks it is empty. Make sure you include this, unless you have customized your CKEditor config to prevent it from eating empty elements. It also helps prevent future content editors from deleting it if they're not sure why it's there.
Then adjust the "height" value. You could also give it a custom class and control your height via CSS, if you need a responsive height. We wanted to keep the module simple and mobile-friendly, which basically meant not setting any heights (apart from the min-height necessary for the slide controls) rigidly. Using the content to set the height means the slides will always be big enough to display their content, so you don't have overflow issues - but it also means you have to choose the image carefully, with the content in mind.
Hope this helps!