Outside Clinic eye tests at home

Just received a letter from a company called Outside Clinic who claim to provide NHS eye test services at home.

Since regular eye tests are free, at least here in Scotland they are, I am suspicious. I don't need their services but there will be housebound people who do .

Should I be suspicious?

I googled and AI report several unhappy customers who felt they were overcharged but not robbed.
How do these companies know my details?