I use my phone one handed a lot. I imagine that would be a lot harder on foldable phones. Are there significant ergonomic differences with using a foldable phone? A foldable tablet seems like it would be a bit easier to use.
I've used a few foldable and of course regular style smartphones. Imo the biggest difference is weight. Ergonomics vary by manufacturer (I think Samsung makes the best specced foldable but actually prefer the Pixel Fold because of how it feels to operate when closed) but in general you're going to have a heavier device if you cram in twice as much device into roughly the same space. I think the people discussing the crease here are right. Foldables aren't perfect, issues like dust resistance persist and battery life can be a thing, but I think the real issue for Apple is that the current top of the line still comes with some stylistic compromises which mean that folding isn't just a zero cost feature to be added.
There's also the types that fold like a book with a second screen on the outside. So when folded, it's like a thick normal phone, but when unfolded it's like a small tablet. I've never quite understand the appeal of the flip-style foldable, seems like the only advantage is taking up less space in your pocket.
