Bender Board and Lawnmower ?

I have an established lawn. The outer edge is brick and the inner edge is wood. The wood is at ground level but over time the wood gets covered with dirt.
The other side of the wood border is a flowerbed. The grass and weeds tend to crossover into the flowerbed and there is no distinct edge or boundary do to the wood being so low.
It seems like over time the wood has sunken, however I think that the ground and grass has just grown over it.
I am thinking of installing BenderBoard that is 5/16" x 3 7/16" x 12'
My worry is if I will have problems mowing the lawn. Currently since the wood edge is so low I can push the mower wherever I wish, it's as if there is nothing there. I would like to be able to mow as close as possible to the edge as possible. However the edge where the bender board will go is not a straight line.
I guess my worry boils down to how high should I install the bender board? High enough to have a distinct edge and low enough to pass a mower over?
Any ideas?
Is the 5/16" x 3 7/16" Fibertech BenderBoard the material I should be looking at or is there something else that will work for my application.
I just bought all the stuff tonight and plan to do it next weekend, however I cold always return the material.

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