I have one on my road bike and one on my gravel bike with no issues. It's been on the road bike for a while, but the gravel bike is more recent. Both see some pretty rough roads. I'm about 94 kg without gear, so they seem pretty sturdy to me. I find it very comfortable so I just put one on my mountain bike as well but I haven't ridden that yet.
Out of curiosity, what type of seatpost clamp do you have? Does it clamp the rails along the full length, or just at one point in the front and one in the rear?