With all honesty, jb is definitely cheaper be it for food/goods and services.
However,
1. Are you comfortable with their eye testing standards and is the prescription given comfortable and feasible for long
2. Do they do extra services e.g eye health examinations that go beyond a simple refraction check.
3. Any adjustments/troubleshooting/servicing concerns means you have to travel back there.
I will ask the consumer if they are alright with it.
For progressive lens users, it is of utmost importance to get proper fitting done and a health check once a year to ensure prescription is okay and health is fine.
If you think the savings of $100-200 is worth it then ofc it is cheap. But for items such as glasses, i would rather prefer doing it in Singapore with a trusted professional. Just my opinion.
I respect those who still prefer going to JB to purchase stuff. Different people have different viewpoints

Just trying to educate a little on why SG prices tend to be higher. - Professionalism and higher rental cost and the machines used to perform these checks.