Filming vertical and horizontal at the same time: what's your setup?

Before ContentCam, my girlfriend filmed every scene twice: once 9:16 for Reels and TikTok, once 16:9 for YouTube. Other people crop one from the other or rig two phones on a bracket.

What do you do now? And if you film your reaction and the scene at the same time with the front and back camera, what have you tried and what broke?

Happy to answer anything about how ContentCam does it.