Actually, the cheap over-the-counter reading glasses one finds in a drug store (here in the U.S.) are just as good as the ones would spend several more dollars for at the optometrist are just as "safe" (whatever that means).
Look, reading glasses, whatever the source are only magnifying glasses… they enlarge the print and do nothing for correcting other visual deficiencies that are built into regular sight correcting glasses.
I spend about $10 (US) for a pair with plastic lenses and durable but plaice frames with the magnifying correction I require for comfort.
The only caveat would be if one requires a drastically differing correction for each eye. I don't and mine are perfectly comfortable, especially since I walk off and leave them forgetfully (that's another story though).
On source explains it this way: "Inexpensive reading glasses typically have the same magnification power in each lens. This is beneficial to people who have the same, or almost the same, prescription in each eye. For example, if one of your eyes requires +1.00 glasses and the other varies slightly needing +1.25 glasses, you can probably get by with a pair of cheap reading glasses from the pharmacy. However, if your eyes require markedly different prescriptions, the best reading glasses for you are custom prescription lenses from your eye doctor. "
If it's any comfort, almost everyone requires reading glasses as age increases. It has only to do with the eye's inability to focus quickly as it did when one was younger… most start in our 20's or so...