Most of the mow and blow guys use something very similar - it's fast and easy, if not the ideal solution. I prefer hand edging myself....:-)

I have a Stihl gas powered edger and it does work well but I find it works best when it can roll on a solid base such as my concrete walk and driveway.
When I tried using it along the grass/mulch area I had to work a little harder in keeping the blade the same depth along the full run.

We hired a gardener last year to do weeds and edging only and they use their weed eater turned on edge. I used to do the same in the grass/mulch areas and once you learn the correct angle and direction to work from, you can get a nice straight cut with it.

Gas trimmers work, but they do so by beating the grass to death- you are left with raggedy ends on each blade that will never have that nice, crisp, healthy look that hand edged borders will have.