Low Search & Solspace Tags
Low Search for ExpressionEngine can work with Solspace Tag to act as a filtering tool. It can auto-generate search urls from a Tag custom field.
Low Search can also generate a "range" filter based on a custom field that is numeric.
ExpressionEngine Conditionals & Parsing Order
ExpressionEngine parses advanced conditionals later in the parsing order than simple conditionals. I blamed this for a template error, but it turned out to be a missing </div> tag.