Generally 'specsavers' etc are franchises,but are definitely cheap,I have used the one in Hunt's cross Asda a few times,with difficult verifocal scripts and always found them sound.
Mrs BB was fucked about by similar franchise in Rice lane Sainsbury's,she persevered with them in a way that I never would,in fact wouldn't touch them with a barge pole.
Their "workshop" branch is in the Swan,so is quicker to get your Giggs.
You,at your age, should be directed to loads of stuff in the £90 bracket,but in reality should be getting 2 pairs for £70.(Without paying)