Kittl is built for the artwork itself. AI image and vector generation, a merch template library, curated fonts with deep text effects, mockups with placement guides, and export in PNG, JPEG, PDF, or SVG give a designer control over the file that goes to print.
That control ends at export. There is no storefront, checkout, or fulfillment on their side: you carry files into a print provider or marketplace and run the selling stack yourself. Commercial rights sit on paid plans, with the free plan limited to personal use, so recheck their pricing and licensing pages before money is the decision.
The tradeoff is the second half of the job. A stronger design tool does not publish your shop, show your margin, or print the order. If the bottleneck is everything after the file is finished, that work is still ahead of you.