I installed the plastic edging on a house I used to have decades ago and didn't care for it. It worked like it supposed to, but I still used a weed eater to clean it up.
The best that I've found is pouring concrete in a small ditch with a piece of rebar in it. But it's also the most work.
I was at a friends house yesterday and they had treated 2x6's flat on the ground with long nails holding it in place on the dirt. I didn't think it would last, but they said it's been there for well over a decade, and in my opinion, I thought it was only in there about a year.
Currently at my house, we are laying thin cedar logs on the ground and using them as a divider between flower beds and the grass. I spray round up along the grass side of the logs so I can mow close to the logs and have it look nice, but not have to use the weed eater.