If you want to fly it indoors maybe. But it's a false sense of security if you ask me.
I think it would be great to have..it doesn't protect you from the top or bottom but it does from the side.
Perhaps not necessary but I think it would be great to have.
I'm looking for a similar thing, so just checking back if anyone has found a good solution?
For my case it isn't to save my hands or walls from propeller cuts, but I'm aiming to provide aerial inspection services (bridges, towers, factory ceilings, etc) and so want to be able to ensure that if I get too close to anything it bumps off.
I figure if you have the protective ring above the center of gravity it should have the effect of pitching the quad away from the contact point, and the APM should stabilize it pretty quick afterwards.
Here's a commercial example closest to what I'm thinking, though in my case I'd want the ring well above the props so it could happily 'park' it on the ceiling with no prop impact - I've noticed with my mini indoor helis that as well as high-pressure ground effect there's a low-pressure 'ceiling effect' so it's pretty easy to get pulled up into contact there.
Personally, learning to fly my quad very recently, I'd love to have protections for flip overs, for rough landings and even side landings !
I think it is very useful because of the number of props I am damaging in my learning curve.
Here is a picture of how I shielded a bit my quad: reuse of helicopter learning ball kit (blue balls on tips of fiberglass sticks), yellow foam on the feet (reuse from swimming pool foam thing), laser-cut protecting arches.
I can tell you that these protections, even though not perfect, saved me already quite a few times!
If you can afford the weight, why not? It can't hurt to have some protection on it. I had my hand cut up pretty bad when my flight controller went crazy due to a short (not an APM - it was a custom board I was designing). I'm with a group that does indoor UAV work and protection is a must. Outdoors, maybe not, but again, can't hurt.
I'm not sure if it's enough benefit to overcome the increase in weight by adding a shroud but maybe I'll get some time to simulate it sometime. I've been plastic printing and laser cutting my own shrouds which work pretty well. Here's one of the designs I use; one of these per arm does it.