I tried an affiliate service called LeadDyno recently for my SaaS. A lot of the companies I looked at all have very similar pricing (starting around ~$50/mo), but not all of them worked with Stripe promo codes, which I needed for my app. I ended up cancelling my account when I found out that affiliates were only getting attributed for the first purchase, and not subsequent charges on the subscription.

Now I use a custom query on Stripe Sigma, which is actually cheaper, but probably won't scale as well.

Anyway, glad to see an open source option in this space. Hopefully my anecdote will be interesting to you. Would love to see support for promo codes in the future.