Actually, the review is correct as stated: it blocks emergency services callbacks. If those said services follow the prompts, they can get through, however, so it is a omission in the review for that point.
As for telemarketers, some DO have the ability to directly interact with the dialer (to hit that 5* combo) if desired. However, telemarketers are incentivized to talk to people who don't want a sales call so much they buy hardware to block such calls, as it likely won't lead to an actual sale. I'd certainly result the call as a "no answer" and move on as quickly as possible. (Yes, telemarketers enter results of a call after each one and nearly all the time pick "no answer," even if you just pick up the line and hang up). Best thing to do is "please remove me from your calling list." The marketers are required, by law, to remove you when requested. Be cordial though, because even then, you might get resulted as "no answer" just to piss you off when their system calls you back after the ~3hr retry window.