Rails can be used to make all sorts of web projects. BulletTrain is laser focused on the tooling for a SAAS, making it much more productive.
It's still a small community using it and you need to be comfortable as a Rails developer to get going and it's for new projects.
I'm using BT for an upcoming SAAS project and it's been a huge boost for the project. The same sense of "oh wow, I could do so much with this" that I got from using Rails to build that little blog demo they used to have on their homepage I got from using BT for the first time.
In general, it's a moving "up" in terms of abstraction. So instead of working with a single form field helper in rails, or even the form field with a little surrounding elements (like simple form). You start working with the entirety of the UX for an individual form field: label, error text, tooltip, placeholder, explainer text, etc and it's very easy to extend. For example, I built a 'markdown' instructions button that is inserted below the label on any form element it's designated on.
- Already a competent Rails Developer
- Building a SAAS
It's pretty much a no brainer in terms of out of the box value.