I have not heard of it, but it is not much of a website and this exerpt is a bit of a red flag:
a rare opportunity to learn from a highly skilled world renowned Korean grand master in multiple arts who is offering Hapkido and specialized self-defense classes in midtown Manhattan is now available to experienced martial artists as well as beginners from the Tristate NY area.
Firstly, nowhere on the entire page does it ever tell me who this guy or gal is.
Secondly, I am always leary "grandmaster in multiple arts" claims. Multiple usually means more than two or three, or if it is only two, they use the word, 'multiple' to suggest more than two.
I also notice that it does not connect the master's grand mastery to hapkido; only that this nameless and genderless individual of presumably Korean ethnicity is a grandmaster in multiple arts who is offering hapkido and specialized self defense.
Now, the school could be wonderful, but if I were seriously in the hunt for a school, this advertisement would not even register on the meter. Now, I may find my way to the school through another means (drive by, recommendation from a current or former student, chance meeting of the GM at Starbucks), but that ad is not a well written ad for anyone interested in more than just location and a few minor details.
Important stuff (name of GM, federation if any, GM's rank in hapkido; his grandmastery may be in taekwondo, what these other arts are, etc.), however, is seriously lacking.
Daniel