I searched "paving stone walkway that is constructed with the rigid plastic retainer strips". Could you rotate the trimmer so it's level with the ground and give the plants a flat-top? Just a little bit lower than the paver tops.

Generally, any rigid edging should be installed with at least 1/2 inch of material above the paved surface. You can go taller if you wish but I think you get a cleaner look if a minimal amount of edging is visible. At that height, the edging provides a barrier that prevents overgrowth of plant material as well as properly retainlng whatever sand or gravel is between the pavers. Or you can leave as is and follow the previous suggestion.

So no, not a great installation IMO.

Your pavers are installed correctly with the right product of edge restraint.

It really depends on the type of (power) edger you are using. You need to adjust the blade depth and the guide width away from the paver edge if you have those capabilities on your edger. If you don't, then you'll just have to eyeball the run or use a string trimmer instead.

Any chance of a photo? If the path is wide enough I personally like the plants to encroach a bit. But not if it doesn't suit your garden style. That said, I'm not clear why a paved path needs an edging. Isn't that for gravel paths?