I heard the same thing. Some say it ran hotter with a regular non-bypass heater valve and some say no difference.
Seems if you want to use the bypass valve, you have to use a separate potentiometer like this one
https://www.oldairproducts.com/produ...ve-kit-50-1555 to control heat.
Or you have to get clever with some wiring to make it work with the VA controls.
There is a version that works with vacuum, but don't want to bother with that one myself.