These physical dividers only challenge weeds to root under, over or around them. Nothing keeps grass or invasive weeds out of a bed. Nothing except cutting a crisp division between the bed and the grass. Plunging a spade along the border of the bed cuts weed roots. It stops them for a time.
Mulches are another landscape budget and time waster.
Especially rock mulches. I saw a new landscape with cobbles along the side of the house and three quarter inch washed rock around the shrubs. It looked like a quarry-not a garden. As long as mulch fulfills its purposes, it shouldn't be a big, costly deal. But mulch can eat a chunk out of a landscape budget.