The one advantage of the drilled mount is that the 4 holes that mount the actual pitot tube will be spaced for commercially available (certified) pitot tubes.
My Dynon pitot came undrilled so the mounting holes I had to drill and tap were in non-standard locations.
If you get it drilled you can then use the holes as templates into your pitot tube.
A minor point, but it costs nothing in this case to follow standards.
