Went to OPSM for new glasses as my PHI said PHI holders get 20% discount. (They don't ask for proof that you have PHI, so I thought this was a bit fishy as they must therefore give it to everyone.)
I brought my own frames as they didn't stock the ones I wanted. Afterwards I checked with the lens prices with a couple of local optometrists. The OPSM lens cost after the 20% discount (high end lenses with extras) was slightly higher than the exact same lenses would have cost from a couple of local optometrists at their normal price. OPSM also charged me for bringing my own frames $40 and $65 for an OCT scan which the local optometrists don't.
TLDR: OPSM more expensive that other optometrists and have a discount that brings the cost down to a slightly higher price as other optometrists for exactly the same lenses (Essilor)
Cool story bro