First of all, you should definitely enquire about the levels they offer (although they claim to be able to offer any level) and the language of instruction for people at your level.
In my experience, "intensive" refers to the number of classroom hours per day or per week, since how much you learn per hour or per week mainly depends on the competence of the teachers, the quality of the learning materials, the other learners (their motivation and similarity in level) and your own language learning abilities. 180 minutes of instruction per day is often described as intensive; super-intensive courses with 6 hours of instruction per day are sometimes offered for people who quickly need to get up to speed in a foreign language, e.g. for business abroad.
I know from a teacher of Chinese who taught both a 3-hour-per-week course and a 6-hour-per-week course that doubling the number of hours of instruction does not automatically double the learning speed. I see two reasons for this. First, when the number of classroom hours increases, it becomes harder to find spare time to study, especially after work. Second, the brain simply needs time to process and absorb the materials, and with less time between the classroom sessions, there is less time available for this process.
I think this is the reason why more intensive courses need to put more emphasis on listening skills, conversation skills, reading skills and writing skills: after a certain number of new words and grammatical structures, the brain is "saturated", so you'll need to do something else. Practising the above skills using the new words and grammatical structures is then the perfect thing to do in the classroom.
So it is possible that you learn fewer words and grammatical structures per hour of instruction, but you should get more opportunities to use them and they should therefore "stick" better. But this takes only the hours of instruction into account. When you are in Japan and if they teach in Japanese, you get an immersion effect that can compensate for the limit to the number of new words etc. you can learn through formal ways. (I experienced this immersion effect when I did a five-week English-language course in the UK without meeting anyone who spoke my native language. This resulted in five weeks of uninterrupted immersion, quite unlike the experience of the many German students there, who often switched back to German after class.) Also, while in Japan, you will be forced to use your Japanese, since it can be hard to find Japanese people who are confident enough to speak English. When you spend some of your spare time with other course participants, try to make sure that you are in a group that does not automatically fall back to English.
All in all, I think the immersion effect (if they teach in Japanese and you get a lot of conversation activities) beats classroom teaching in your own country. However, two weeks is very short; I would recommend courses that are four weeks or longer. You should also consider whether you know enough "survival Japanese" before taking the plunge; otherwise you may find yourself trying to switch back to English whenever you can.