The teacher in Mr. Michael's Academy uses many other creative ways (involving all five senses) to teach kids the language. Kids love it, --- some didn't want to leave after the class. :)
No, you don't need to buy the Oxford Path materials. They are offering summer discounted price right now, and I think the price now is about HK$260/per lesson.
They have a new designated center to teach the playgroup, by one of the book writers. It's Mr. Michael's Academy in Jubilee Square, Fotan. It's really good.