My wife and toured for two days with Ho Ho Go, one on Hong Kong Island and the other in Kowloon, with two different guides, both excellent.
We came to Hong Kong with three days available for guided touring and an ambition to learn a great deal about history, culture, and present-day life. (We were willing and able to explore the food and nightlife on our own.) We were put in touch with Ho Ho Go through a knowledgeable travel professional, who recommended them based on this spec.
Once in contact, Ho Ho Go was more than willing to discuss options and itineraries, and ended up proposing plans to us that matched our priorities beautifully. Each of our guides knew a great deal and was responsive to our wide-ranging questions. And each was a pleasure to be with, knowledgeable, smart, warm--important when two of you are spending an entire day alone with one guide.
I won't go into the specific itineraries, since they reflected our particular interests--I will say that we could not have asked for better with respect to the approach (e.g. mix of public transportation and walking), pace, depth, breadth, and openness to discuss issues of some political sensitivity.
We did not experience Ho Ho Go's group tours, but we would certainly recommend anyone wishing to learn more than the superficial about Hong Kong will do very will with this organization.