I use one of the biggest ones they ever made for Echo. I don't know if it was for blade use or what, but it's easily twice the size of the current shields. I keep it for these reasons - and yes, this has been beaten to death -:
1. I learned how to edge/trim with one on and simply continue to do it like that.
2. When I take it off, it seems I have to use more force to hold the head down, so you could say it serves as a partial counter-weight to the engine. Especially when working on slopes and trying to "one arm it."
3. I love the blade to cut the line. Mine came with two sets of holes and I use the closest to the edge. There's room for a third set, but just have never gotten around to drilling the holes to give me that extra inch of line.
4. It gives added protection to close to the ground shrub growth when edging a bed. It's not perfect but I mutlitate a whole lot less shrubbery/plants with it on than off.
5. Deep down, while I know it probably would mean nothing, I feel if I were to break a customers window or passing cars' window, I could at least point to the shield as an example of me trying to follow the suggested safety guidelines and use it safely. Like I said, this may mean nothing, but...
6. I think I get hit less than without one, but if you get hit 10+ times a day, preventing a couple of more just doesn't seem like that big a deal.
7. No one else in my company likes them, so I can rest assured the little ******* will never grab mine "by mistake."