It is pretty useful and convenient if your use case suits it but I don’t think that fits the majority of people. For me my Fold 6 replaced my Kindle and Surface. It’s nice to able to open it up to read ebooks and manga since opened up, it’s pretty much the dimensions of a typical book. Also makes things a lot easier when I need to remote into a PC or SSH into stuff and is a really convenient sketch pad for ideas.
It’s also really neat that it’s not ridiculously wide like every other phone out there nowadays since I have small hands.
My Fold 3 lasted 3 years with no issues until I traded it in so I think they’re fairly well built.
In this case with the trifold, I personally think it’s way too big but I’m someone who’s never seen the point of tablets that were larger than 7 inches anyways. Always preferred a laptop at those sizes.
