No, to my thinking to learn English in three months and ten days is a very effective advertising campaign but I wouldn´t hold my breath yet. It´s not the cure-all to those that are going from 0-60 mph in just 2.3 sec. like a Porsche 918 spyder.
So, no course or magazine can guarantee that and delivery, what one can do is to help one find their way by tutoring, by making the necessary corrections, etc.
The good news is, one can do a lot in a hundred days, can learn a lot. That means that he being surrounded and immersed in the right environment, he will learn wonders!
Yes, this way, and with some discipline, the learner certainly will get a measure of skills, that might be enough to his speaking and to communicate, express himself.
To set up a time, though, is something that can derail the learning effort of many students, by shying them away from communicating (am I doing well? what if I am not?).
Back to the miraculous English magazines, they generally offer the basic of the basics (with some exceptions - I had found good ones more than once); I know that because I myself have bought some of them in my beggining days.
It´s not that they are bad in itself, but with time it gets repetitive and you want to grow and go to higher heights.
I am thinking, of course, of the learning on the long run. Just think about how many things you have learned in a year, two, could it be compressed in a hundred days?
It´s just my view, though. Others may disagree.