There are a couple of things to bear in mind:
the quality of optometrists is governed by their own professional body, so they all have a high level of basic skill, but some are better than others. Where the division lies between adequate and excellent lies in their ability to communicate with people, their patience and so on.
Specsavers is one of many chains that because of their size end up relying on locum optometrists - there is so much work that the original person who opened the branch is either putting their feet up, or just too busy to see everyone. So naturally you may (only may) get less excellent service from a locum than from someone who owns and runs a practice. I find my local specsavers optometrists are excellent - but I won't buy my frames or lenses there. I just have the eye tests and say thank you. I do however get my contact lenses there.
Always ask for a copy of your prescription when you have had an eye test. It is your property.
You are free to buy your lenses and frames or your contact lenses anywhere. Some practices try to move you slickly on to their dispensing optician (the person who flogs glasses to you) with an implication that 'now you should select.....' but don't bow to that pressure. if you like what you see, have it, if you don't , take your prescription and shop elsewhere.
(to be continued)