A few cons to consider:
Private schools will already have finished, plus anyone with only GCSE and/or A level aged children so there is still a fair amount of competition for holidays on those dates so there is less likely to be a significant price differential than with e.g. a random week in June.
It may be an extra headache for people who live close to borders where they may have children attending school both in Essex and other areas that don't have the same holidays which could mean they have to cover extra childcare weeks.