My completely honest feedback would be to look at Ernest Aves in Ware. Although they are not in Hertford, a lot of people in Hertford use them as they are excellent. If you had asked for a recommendation, this thread would have almost unanimously stated Aves.
I have used them for 18 years and cannot fault them (and wouldn't leave them, sorry). They are your main competition.
Obviously their staff, service, products etc are excellent but it is also the little things like free fixing of my glasses when I have bent them (supplied by them), and similar.
However not all people use them and there are new people arriving in town so if you can match Aves in terms of service, customer care and products you could do very well