In various forms, for various projects, and to various degrees, I've worked with or come across them over the years. They have earned their excellent reputations.
But they're not always the right fit. If all you need is company formation and maybe some basic accounting/management, you can find better value elsewhere.
Go with them if you're looking for tax planning and other more sophisticated arrangements, where you want to be absolutely certain that each step is taken correctly and your structure is sound. They will very often insist on providing directors an even nominee shareholders.