The key to success in Open Source lies in understanding that it's not just about software, it's about the people.
It’s very hard to make open source work for products. multiple problems:
How is it funded? could still make money from services, but makes it harder to integrate and sell. as a user, you should want this app to be around for the long run, and the best way to ensure that is to fund it directly.
Open source doesn’t guarantee long-term viability. it’s extremely common in OSS that maintainers burn out, things start breaking, and there is a lot of churn (until it dies).
While it’s true that development might go quicker, a lot of the time the overhead of managing the open source workflow negates the wins. And sometimes the problem just takes a while to think about, no amount of throwing devs at it will help (this is the case for what I’ve been doing in the past several months. Actual’s architecture for local data + syncing is unique and required careful thought). Open source works best for libraries in my experience. I think the best thing I could do is open-source parts of the apps as libraries, which would share the work and allow people to contribute back, while still allowing Actual itself to be carefully integrated.