Rocky is our resident professor Emeritus of all things Parker, but I'll throw in my two cents worth.
They make an excellent boat. Very high quality. My only complaint is that the shallow draft boats slap pretty hard in the chop as you might expect. I recently discovered that they also make the 21' with a deeper V-hull, and I would recommend it, unless you really need the shallower draft.
Jack White at 3A marine in Hingham is a great guy, and a good source for Parker boats.
Jay