Broomfitters

Reqmunk is exactly what we were asking for to require an add-on at checkout. In our case, we needed a way to attach a required shoe accessory (which is required for the curling shoe to function properly) to a shoe purchase while keeping both sides SKUs intact. It's not a bundle and it's not an upsell. It's a *requirement*. This app saves us dozens of uncomfortable "sorry, but your order is actually more expensive" follow up emails to customers who missed instructions in a generic bundle app.

This app seems to be abandonware at this point.

Support has been excellent and super responsive, with the developer implementing new requested features to match my needs within a day or two. The app is really powerful, and has let us build our affiliate program in a way that is both out-of-the-box and exactly to the needs of our program. We're not pigeonholed into a one-size-fits-all model like Collabs. (Aside from dealing with PayPal) the automated Stripe and PayPal payments are a massive win for our program.

The integration between Printful and Shopify is smooth enough as to almost be transparent. Super easy to build items on Printful and add them directly to your store.