My youngest was a helmet baby! I felt guilty for a bit when I found out just how severe his flat spot was. But it was either get the helmet so he can have a round head or leave it and let him have issues with ill fitting headgear and no short haircuts his entire life. He spent 99 days in it and while sleeping was tough, while he was awake it didn’t bother him in the slightest. I have absolutely no regrets doing it and if I had to do it all over again I would! The few months they spend in it is nothing compared to their entire life 
My son also had Plagiocephly. The helmet corrected his problem.