Go locally. I have had good service from Alders, although they are a bit more expensive. A friend of mine just recently went to Spec.Savers. She wears varifocals. After the due tests etc., a prescription was made out for new ones but she had to wait two weeks for them. On picking them up from the shop she knew they were not right and said so, but was told that as the prescription for them was stronger in some respects she would probably have to get used to them. She took them away but after a couple of days just had to return them because they were giving her headaches. When they were examined by the Optitian he said immediately they were not right and they would have to be replaced and that would mean another two weeks waiting. My friend decided that she would have her money back and go elsewhere. So not a good experience at Spec.Savers.
...similar story for me, I have had to have a re-test as prescription not even right so many things have gone wrong, other half gave up and bought from Spex for less and is really p[leased with results