Tempo Next Percent owners, is it ok to wear these shoes on a fine gravel trail?

It is okay.

They will be damaged quickly. Avoid it

There's been ultra runners wearing them on pretty runable trails, you'll probably just wear them out quicker.

They aren’t great on anything even remotely uneven in my experience.

For a race, yes I would. For training, no. They will wear them out faster. But if racing, I would all day long. I haven't yet in my pair. But I have in my Endorphin PRO's. They hold up very well during 50k's for sure. And would wear them for 50/10milers as well. If going at a good clip.