I have sunk some blocks into the soil between the grass and the flowerbeds so I can mow over them. It's called a mowing strip, but it can be made of patio slabs or house-bricks or probably lots of other things. Saves trimming the edge of the grass
Don't put the green plastic stuff in. I did that. It took me ages and it was useless. It bent over and the grass grew over it, eventually. I look forward to some decent answers on here.
Agree about Everedge - I've used it with great success, but it is incredibly expensive for what it is (galvanised pressed steel, painted). It's fine if you have a tiddly border to deal with. The clipping together is clever (and patented, I suspect).
Next time I'm in for DIYing it and used mild steel strip from a engineering company and having it plated. Then bolt it together.