I understand your fear.
I like flat bars. They have a different, more “friction” and “hollow” feel but I have always liked them. Then I had a pair of skis that just fought me (I think edge high pair). They made me terrified of flat bars. But that was just the skis. I got over it and back at it. But because of that, I can understand.
I think if you get too used to mailbox/tubes, you get an unrealistic idea of how slippery rails are. Flat bars/shotguns were actually always easier for me because I felt I had time to feel the rail and set a spin. Flat bars especially. They’re how I learned back 2 outs
The 90 degree edge on each side allows you to bite into it and set a spin, whereas a tube/mailbox isn’t as easy to learn to bite your edges on. It’s a delicate balance and the fact that you can dip on and off the edge on flat bars helps a lot.