Re: not quite a prop guard but....
I am working on something to protect props in a light ground tip over. Not really a prop guard. I call it a prong. It is like the skag on the tail rotor of an OH-58 Kiowa, keeps the blade out of the dirt but is not bullet proof.
The prong I am working on consists of a 3D printed ABS snap on component that goes over the motor nacelle and uses the counter bored screw head recesses underneath to index it and maintain orientation. It does not use screws, just snaps on and locks into the counter bores on top of the screws.
It has a slip in carbon fiber tube to guard the prop. The current weight of one is about 10 grams, this may change a little. That would be 40 grams per set.
It would not be able to eliminate damage if you fly into something, just let the props spin if it tips on landing. It may change in the future.
Kengineer