That best rated consumer reports detector only detects fast burning fires.
The Nest Protect, for example, has both slow burning and fast burning smoke detectors as well as carbon monoxide. Three detectors in one. They also have built sensors and perform weekly automatic self tests to ensure they will make noise/alert when needed and that the detectors are working. A non functioning sensor in a detector just provides a false sense of security. Just about every time there are deaths from house fires detectors are either missing or are non-functioning.
Speaking of non-functioning, many people disconnect detectors because the cheap ones are so hard to silence if there is a false alarm. Again with the Nest Protects you just wave at them. People are far less likely to disable something if it's not annoying.
When there is an event instead of just loudly beeping, they also speak in a clear voice what the issue is (smoke, CO, etc.) - and more importantly, which detector is going off so you know where the issue is as well. I love that for my parents who are older - clarity in a time of crises is life saving.
So yeah, at $100 (easy to find them on sale or bundled) they cost more than a $31 detector - but they also do a hell of a lot more. Having had friends/family who have had to deal with house fires in the middle of the night (very disorienting) or near death experiences with undetected carbon monoxide (it's more common that one would think!) the slight price increase of them is WELL worth it. A ridiculous pittance for the greatly increased peace of mind.
And they still work without connecting to the Internet. I would at least do it initially to configure them, especially to program in their locations so you get useful information in an emergency, then disconnect them if you are really paranoid. However I do like the alerting if there is a problem with one. It happens - sensors don't last forever and I'd rather know about a non-functioning detector and replace it rather than have a useless piece of plastic on the wall.
Also love the motion activated path light feature of them too - so perfect for moving around at night without waking others or having to fumble for a switch. Wish they had an option for brighter lights, especially for units in the hallway - or as supplemental emergency egress lighting. Would help further offset their higher cost.
But yeah, smart detectors - probably one place where there is SIGNIFICANT net benefit well worth the increased cost.