I've used some of the ~3.2m ones from Screwfix and they seemed fine - there was a little flex in them, but that is to be expected I guess. I'd be happy enough using them indoors for painting and going in to the loft

. Certainly very handy for carrying round. If I was travelling and doing jobs, I'd certainly use them.
However, I needed some ~5m ladders to access a double height roof void and had a look at the ones for sale on Amazon. Some of the comments mentioned problems with rigidity and the base looked very narrow - so I passed and bought some large aluminium extension ladders instead.
If you do get some, I'd be sure to get some from a good manufacturer. Personally, I wouldn't trust some of the no-name brands for long length telescopic ladders.