Cost per click was more common in the early days of affiliate marketing but has diminished in use over time due to click fraud issues very similar to the click fraud issues modern search engines are facing today. Contextual advertising programs are not considered in the statistic pertaining to the diminished use of cost per click, as it is uncertain if contextual advertising can be considered affiliate marketing.
The downside is that Shopify is only appealing for people who have physical or digital products to sell and have a need to set up a Shopify store, including site hosting, payment processing, and all the other services offered by Shopify. This can significantly narrow the appeal for this affiliate program. But if you can distinguish yourself by educating people on how to use Shopify, how it can benefit their business, and/or make them money, you could potentially big money via the affiliate program. Add in the 2 x monthly fee commission rate, and landing just a few sales of their mid-tier and top-tier products can result in significant earnings.
You'll also need ecommerce software, fulfillment software, worry about warehousing, customer service and refunds. But that's not all. You'll also need traffic. Think search engine optimization, Facebook ads, and other social media campaigns. It is hard work, especially on your own. You could opt for Amazon's platform, which might be the easier route. But, then again, at the end of the day, this is a serious business, which could produce significant profits. So you're either all in or you're not.