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.
The online lead generation is a multi-billion dollar industry. Done right it can be far more profitable than many imagine. Everyone that I know that is in the business and knows what they are doing, for the most part, does 6-7 figures. While that's a huge range, much comes to one's ability to scale and effectively build / manage the infrastructure needed to scale.