A British Citizen can live and work in Ireland without a permit. Once lived in Ireland for five years, a British Citizen can apply for Irish citizenship.
If Leaving Bro wished to move to Ireland with his new found British Citizen passport, then that is his choice. The advantage of Ireland over other parts of the EU is that Ireland is an English speaking country which can make life easier for people from Hong Kong. On the other hand, it is difficult to find a job in Ireland. Leaving Bro can try and get a job in a Chinese restaurant.
Life in Ireland is not like Hong Kong - it is hard, but if you have an aim (getting Irish citizenship in 5 years), then it can be easier!