Hey Mark,
I dont subscribe to that theory at all. I think it is pretty average Spin actually from Facebook gooses. Unfortunately if it is said enough, Myth can become belief. It is a shame a trained Mechanic cant distinguish the difference though.
It boggles belief that a Trained Mechanic suggests that a HiFlow Water Pump will cause the water to travel too fast through the cooling element. Shoot that bloke! he is Brain Dead.
The Hi Flow water pump is designed to provide Pressure to the flow, the Pressure in the flow will ensure a strong delivery of cooled water when the Thermostat Opens........ The bloody Thermostat will determine how long the water takes to flow through the system and when it is cool enough. The idea is to ensure there is little to no cavitation and the water, when released by the thermostat, flows efficiently and quickly to where it is needed. When the Thermostat feels the temperature change it closes and the Water pump cycles on.
To suggest that the Hiflow pump wont let the water sit in the radiator long enough defies basic physics. When the Door is closed (Thermostat)the cyclone stays Outside and the air inside your house remains calm... you open your front door and your back door and you will get knocked over, Close the bloody door and it is over.
Your Hiflow pump looks like the JPC Pump and i run this pump. there is a guy on FB that makes his own design and his testing suggests his is slightly better but IMO the Jury is out on that. This is a good unit and you should fit it with confidence.