Though some more reasonable forms of this idea exist, this particular description has some major problems:
* What if the money you pay someone does not go as far as expected? Maybe they lose some of the money in various ways, or maybe they are just very bad at negotiating economic transactions or buy the wrong kinds of things from the wrong places. Maybe they are trying to live in an expensive area -- do we kick them out?
* There will be a significant class of people who simply know nothing at all about work or participation in the economy. That may have all kinds of bad effects for those people, one of which may be a greater likelihood of the problem above.
* Some people who would otherwise be productive will put off both education and work for a while. When the time comes that they want to be involved, it will be hard for them to make the transition, and many will just stay out of the workforce forever. So, some of the ultra-productive people the author is expecting to do the heavy lifting will not exist.
* There will be pressure to stop granting new citizenship/residency to almost anyone, because the potential cost will go way up. Even if, in the long term, immigrants are good for the economy, in the short term it could be crushing if each one gets a comfortable living regardless of work.
* There will be an imbalance in which jobs are actually done. The number of computer programmers might be higher, but the number of nurses might go way down. If having a nurse is required to make some people comfortable, how do we remedy that?
* "Comfort" in general is a moving target in this process because changing the basic income will have a big effect on the economy. It's hard to say whether you could ever really find a stable value that offers anything resembling "comfort" for those living on it.