I would recommend checking whether it is well-thought in the area you do care about.
I was surprised to find out that you cannot easily save PDF from a webpage to reliably keep it on the phone forever; it will be subject to cache retention policy. There are more obvious limitations, of course. Nobody is free of mistakes, so check what is obviously important for you in the specific device you are going to use.
Is this using Safari? The iCab mobile browser is a couple bucks, but infinitely more functional, including durable saving and adjustable ssd cache. There are also lots of good reader and filer apps.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: