Late to this thread, but I've often wanted a string trimmer with reversible direction of spin - *not* for "handedness" or direction of walking, but because, over time and repeated trimming of the same areas of the lawn, the growing grass seems to take on a set swirl pattern in the direction of trimmer spin.
If you could reverse spin direction, the cutting in the opposite direction from the swirl set that the grass has taken makes the cutting much more efficient, *and* would actually prevent the growing grass from taking a set in the one direction.
When it takes on that swirl pattern, it's more or less laying down close to the ground almost parallel to it so the grass blades tend to stay too long, and if you lower the trimmer to get the grass blade length right, you end up scalping it. Another way of saying it is you end up losing control of simultaneously getting the grass blade length and height right. I found this problem is particularly bad with fine fescue that tends to lay completely over once the blades get beyond a certain length anyway, compounded by it taking a trimmer spin direction set, which both feed on each other so it never recovers unless you manually rake it in the opposite direction before trimming - not good use of time.
So - if I had a reversible trimmer, I'd typically alternate spin direction with each trimming session, or according to noticing the grass taking on a definite swirl pattern in one direction, which I absolutely see with my unidirectional trimmer.
I was a little surprised that no-one brought up that problem in the course of the thread (which, again, I'm just seeing for the first time).
