Took me almost two weeks of daily practice before I lost the gag reflex.  Apparently, it doesn't come back with time.  Some thirty years later I surprised the endoscopy staff when I insisted that I not be given any anesthetic for my upper endoscopy.  It went all the way into my stomach with no gagging.

Sean Lockhart (aka Brent Corrigan) is a perfect example.  He was 6.5" at the start and grew to 7.5" in about a year using a vacuum pump. He didn't seem to suffer any ill effects.

I have been using a Flowbee (https://www.flowbee.com/) for about a dozen years.  I trim the edges (sides and back) with a regular electric hair clipper.  I am an attorney with wavy hair and have received compliments on how well groomed I always am.  The Flowbee is fast and easy to use; it vacuums up all the cut hair.  It has paid for itself many times over.  Do it in your own home, at your convenience and as often as you wish.