When I first got to my current school they were using these for trumpets and trombones.
I was skeptical at first but they actually work really well and my kids like using them.

We have school trumpets and trombones so they all match for marching band. Silver.

I haven't really noticed any damage to the instrument other than some light scratching on the bell. But they're silver and light scratches really aren't a big deal to me.
I haven't had any issues with it bending the bell.

Just know that there are ones for Trumpet, mello, baritone and ones for Trombone. The clamps are on opposite sides. You can't really use a trumpet one on a trombone and vise versa.

If your trombone players are struggling holding the flip folder with their left hand, these clamp flip folders are great to have!

My trombones and trumpets do like to have pages for each song in our folder so they don't have to turn the whole flip folder around and re clamp it for each song.

I have regular lyers for mellos and baritones.
I like the clamps for trumpet because the trumpets I have don't work well with a regular lyre.

good luck and do what works best for you, your kids, and your instruments!