The 28 day free trial is for Magento & custom platform. Tagalys is a free app for Shopify merchants.

No credit card required to start our free trial. Just signup, get API keys and proceed. 

After your free trial, you will automatically be assigned a plan based on your usage pattern (number of searches/pageviews/impressions/sku count).   

You can always upgrade your plan if you need any additional features that meet your business needs.