TL;DR: hair colour turned out well, don't book first thing in the morning, treatment was quick. I'm not convinced I would go again.
Long review: I booked an early morning slot via Treatwell. On hindsight, this was a mistake as the salon had barely opened when I arrived. One stylist was attempting to do everything (she did a good job with my hair) whilst the others arrived 15 - 20 minutes late*. *Late = assuming Treatwell opening times are correct.
The stylist manning the desk on her own seemed stressed and frustrated that I was there so early. She clearly was not ready for me, even though I had booked days in advance. The resulting exchange was awkward for both of us.
During the treatment, an assistant came by to "sweep up" hair from the day before with a hair dryer. Using a hair dryer to do this released the hair from awkward corners. It also came with the unfortunate side effect of blowing it everywhere.
Note to salon - please don't use hair dryers to brush up / collect hair from the floor whilst a client is having a drink (ever). Esp. short hair will blow into the drink...
Colouring & treatment itself was excellent. I have received plenty of compliments since my visit.
To close: decent service, avoid early morning visits.