Like many things in sailing wing keels are a compromise. Properly designed they afford similar stability to a full depth fin but at the price of greater weight, greater drag, a slightly quicker motion and less windward ability. Adding to that problem many wing keels are not all that well designed. I am not familar with the CS Merlin''s keel.
Then there is the issue of running one aground. There is a perception that running on aground in mud or while heeled over can jamb you in a lot worse than with a conventional keel. In a BB discussion with people that have wing keels the mud problem seems to have more validity than the heeled over and grounding problem.
Still if you need shoal draft, a wing keel may be one of your few options.