If you put a fan on the left side of the extruder, you have to be careful not to run into anything when you zero the X-axis. Often, you must put on new stop of the X-axis limit switch to keep the fan from running into the printer frame, etc.
I “mirror” printed a regular right-hand fan and mounted it on the left-hand side. I then attached a small blade to trigger the limit switch ~0.5 inch further out.
The few extra mA draw of an additional 40mm fan is tiny compared to the big amps that the heater draws. They also have two fans on the dual extruder as well as the new Taz6. The fans are simply wired in parallel.
You will really like the nice prints you get with even cooling from two fans. I have two fans on my flexistruder.