I have used Robertson's in Central (99 Queen's Rd, Central). The process is simple, if uncontested, and legal costs about $20,000. Once the papers are served, it will take 3 to 6 months for the divorce to be processed. The advice they gave us was to sort everything out before filing for divorce, including dividing assets and making any cash disbursements. That way it is easier on all.
I went to Family Affair Office at The Inland Revenue Tower in Wan Chai. I only paid approx HK$3000 for filing of the papers and the fees. I heard some ppl pay a lot of money. In my case we have no kids and no property to split. So maybe thats why.