Our shop is an active shop in regard to both new open water certifications and advanced technical training. Most of our OWS instructors also have some form of tech certification and/or are tech instructors. We rent and sell both jacket style BCDs, SM systems, and BP/W systems, so we really don't have a particular financial reason to promote one system over an other. That being said, we have learned a lesson or two about skill demonstrations so we've developed a unified approach.
Our current mindset is that new open water students have enough to worry about and learn without having to make mental adjustments to demonstrations. Yes, a good instructor that is used to his gear should be able to easily remove and replace a weight belt that has been woven under his crotch strap, however, that demonstration provides little to no value to new students that need to know how to remove and replace weight pockets. Therefore, we use a jacket BCD for our confined water demonstrations so we can demonstrate the skills close to or identically to how the students will be doing it. We then use our "favorite" gear whether it's a dual bladder side mount harness with a single tank and/or BP/W for open water dives since we rarely, if ever, need to demonstrate skills during the open water dives.