The simple way to decide
If the next project is SMS, choose Postscript. If the next project is a simple Shopify newsletter, use Shopify Email. If the next project is serious email automation, compare Sequenzy with Klaviyo, Omnisend, and Drip.
Where Sequenzy fits
Sequenzy is the useful middle path when Shopify Email is too limited but SMS is not the real priority.