This extra is a MODx version of SmartOptimizer by Ali Farhadi (http://farhadi.ir/works/smartoptimizer), a PHP library that enhances your website performance by optimizing the front end using techniques such as minifying, compression, caching, concatenation and embedding.
Hey,
I discovered that changing the setting of smartoptimizer.cache_dir has no effects because in your code you query
$modx->getOption('smartoptimizer.cache_path')
Changed it to smartoptimizer.cache_dir in two places, works now.
Thanks for the plugin and your help!