* We demanded the same or slightly less time in total than other conventional-interviewing companies did.
* The scheduling of our demands was totally flexible, unlike interviews, which are rigidly scheduled. If you're a morning person, and you have next Tuesday free, that's when you threw the 2-odd hours you needed at the challenge.
* Obviously, it's easier and less stressful to put effort in from your couch than in an alien office environment with people staring at you waiting for you to answer properly.
* The challenges themselves were fun. They were real work: we didn't have people literally slaying dragons (they were breaking a web app and a client/server app), but they were the distilled enjoyable essence of that work with most of the BS removed. In fact, if you didn't find the challenges fun, that was a huge signal that we were the wrong job for you.
* If you did decide we were wrong for you, you could stop at any time --- randomly, on a Tuesday night, with a slice of pizza in your mouth --- and have none of the weird social pressures that would make you sit through a string of pointless interviews. Which is an experience I have had, more than once.
Regarding certification: pure, chill-filtered hatred of certifications is what got me into the part of software security I wound up in. There is zero chance that we are going to build something with the market dynamics of a certification.