There seem to be an explosion of online behavioral tracking tools, the default for most companies being Google Analytics. Its hard to find real reviews of these systems - Two I'm looking at are for more advanced featuresets, including Snowplow Analytics, and Adverity. Would love to hear any reviews about these, or other SAAS in practice, challenges, or otherwise, or other recommended tools. This includes tracking, ad performance, optimization, attribution, segmentation, filtering, storage, visualisation, APIs.