TL;DR: Chip in the hair, didn't listen to what I said, and didn't feel valued as customer.
I thought I would go for the cheapest one (£2 difference) because I have an undercut and they literally only need to do my sides.
Aside from not spending more time on the hair (the whole procedure took 8 minutes with brushing) there was a chip found (resulting in an uneven shape) and the hairdresser didn't cut to the size that I asked for (shortest possible)
This was after the manager had a chat to let me know that I needed to pay £4 extra for the fade (which they might as well have done since they were only cutting my sides, which is £2 extra on treatwell) When I said I'm fine, the hairdresser literally finished this off in 8 minutes, didn't put the machine setting to what I asked for (the hair wasn't as short, so I'm assuming I'll have to come back sooner) and left a chip on my hair.
I will need to get the hair done again - but never at this place.