I evaluated Bullet Train last year when building an MVP for a client. Ended up using Jump Start Rails instead. Main reasons:
1. The hybrid approach to iOS and Android apps with JSR were better than what BT had to offer
2. There was a lot less to learn about the mental model of how JSR was built via Bullet Train. It was basically pay, pull down, configure, and get going with JSR. BT has things like SuperScaffolding, an abstraction layer on CanCanCan, etc. I didn't want to have to ramp up on those to decide whether they were better than the alternatives.
YMMV of course. JSR is a paid app and IIRC BT was at the time too... but looks like maybe not anymore?
1. The hybrid approach to iOS and Android apps with JSR were better than what BT had to offer
2. There was a lot less to learn about the mental model of how JSR was built via Bullet Train. It was basically pay, pull down, configure, and get going with JSR. BT has things like SuperScaffolding, an abstraction layer on CanCanCan, etc. I didn't want to have to ramp up on those to decide whether they were better than the alternatives.
YMMV of course. JSR is a paid app and IIRC BT was at the time too... but looks like maybe not anymore?