If your feet need support, they don't provide support. So pretty much what you would expect: ankle pain, shin splints, soreness, etc...
My problem was the opposite: I got shin splints even after spending a ton of time stretching my legs before and after long walks, running. But I started to notice that my feet felt a lot better whenever I was barefoot in my house, and that I had fewer problems during the summer when I was more likely to take long walks in low-support footware like sandals or flip-flops. So when I noticed that the support was the problem and got rid of the shoes that had thick heels and lots of cushioning, that pain went away.
Basically, if normal shoes hurt your feet, there's a reasonable chance (but not a guarantee) that barefoot/low-support shoes will be a big improvement. If you normally prefer lots of support to feel comfortable, there's a reasonable chance that these will hurt your feet.
There's also a bit of an adjustment period. You do feel more of the ground, and it takes a little while to get used to that. If I step on a really sharp rock, it won't puncture my foot or anything, but I feel it. Your walking/running style ends up changing a bit as well to accommodate less cushioning, you spend more time on the balls of your feet instead of your heels.
I haven't taken them hiking, but if I was a hiker I probably would at least consider wearing them over normal boots (or more likely, I'd get an equivalent low-support hiking shoe). I like that my feet are more flexible, I like that I can feel the texture of the ground, it makes me feel more confident and secure when I'm walking over rough terrain -- the same way that I feel more confident manipulating something with my hands if I'm not wearing very thick gloves.
But all of that is just me, your results might vary.
My problem was the opposite: I got shin splints even after spending a ton of time stretching my legs before and after long walks, running. But I started to notice that my feet felt a lot better whenever I was barefoot in my house, and that I had fewer problems during the summer when I was more likely to take long walks in low-support footware like sandals or flip-flops. So when I noticed that the support was the problem and got rid of the shoes that had thick heels and lots of cushioning, that pain went away.
Basically, if normal shoes hurt your feet, there's a reasonable chance (but not a guarantee) that barefoot/low-support shoes will be a big improvement. If you normally prefer lots of support to feel comfortable, there's a reasonable chance that these will hurt your feet.
There's also a bit of an adjustment period. You do feel more of the ground, and it takes a little while to get used to that. If I step on a really sharp rock, it won't puncture my foot or anything, but I feel it. Your walking/running style ends up changing a bit as well to accommodate less cushioning, you spend more time on the balls of your feet instead of your heels.
I haven't taken them hiking, but if I was a hiker I probably would at least consider wearing them over normal boots (or more likely, I'd get an equivalent low-support hiking shoe). I like that my feet are more flexible, I like that I can feel the texture of the ground, it makes me feel more confident and secure when I'm walking over rough terrain -- the same way that I feel more confident manipulating something with my hands if I'm not wearing very thick gloves.
But all of that is just me, your results might vary.