I have been going to Headmasters every 6-8 weeks for about 18 months. I first went because the opening times suit me - they are open til 9pm during the week, so I can go after work rather than having to take time out of my weekend, although they are also open on Saturday and Sunday. I kept going back because my stylist is brilliant and completely understands that I don't have loads of time to spend on my hair (that a quick pass with the hairdryer / straighteners is as much as I can manage in the morning), but that I still want to be able to mix things up with different style / colour techniques.
In general terms the staff are helpful and always try to fit in appointments, even at short notice. One downside: although the decor is modern, some of the fittings are tired and could do with replacing. However, that is more than made up for by the atmosphere and I have been happy to recommend Headmasters to my friends in the past.
In terms of cost, it has always been on the pricey side but with good discount offers throughout the year. However, they have just introduced a new really competitive price list, so now I don't even need to wait for the discount!