Let me start by saying that I won't criticize here the quality/sharpness/etc of the images that are obtained after using this filters because I am not an expert and because I don't know what a $500 lens can do for you in terms of quality. Instead, I was very satisfied to test by myself that a $10 product like this can produce useful images.
My disappointment comes from the observation (see my posted pictures of an orange pepper) that the magnification is almost impossible to notice using the filters +1, +2, and +4. I started noticing some meaningful effects only after I applied the diopter +10. In fact, only after I screwed simultaneously the 4 filters I was able to produce a x4 magnification of the subject (as shown in the pictures posted).
The advertisement pictures that have been included which show an insect actually get larger and larger with each increase in diopter are in my opinion exaggerated and misleading. This doesn't make the product bad, just "not as advertised", but for 10 bucks I would still buy these in order to have something to play with until somebody offers me a job that can pay for the 500 dollars needed to buy "the real thing".