I imagine it's not always like this, but my visit there was kinda chaotic. It seems some of the hairdressers fell out unexpectedly, and the rest somehow forgot about the treatwell bookings. I ended up waiting for 30 minutes and was finished off in around 20 minutes.
In the end, the shape of my haircut is quite good, it's just visibly rushed. Plus the waiting, and being forgotten about. Hence the (pale) 3 stars.