I really hate bright sunny burny days, so on a bit of a whim bought the Gossamer Gear Lightrek Hiking Umbrella from BPL. It's only 187g.
I got to try it in both sun and rain, on a recent 3 day hike in Mt Buffalo.
Sun: Pretty great. It was really nice being able to take the hat off and open a few buttons on my shirt for better ventilation. I found I wasn't hunting around for shade every time we paused for a few moments.
Rain: Also really good, in these fairly light showers with no wind. Much better than stopping to put on a rain jacket and then take it off again. It was also really helpful being able to do stuff on my phone without the screen getting wet.
It seems to be pretty solid, and I like the way it doesn't collapse down. There's no telescopic pole, or hinges, which I think compromise durability.
I'd like to see if I can find a good way to attach it to the pack so I don't need to hold it. I found a bodgy method that at least meant I could do things with both hands while standing around, but it wasn't quite stable enough to walk with.
It's also nice being able to temporarily share some shade or rain protection with your hiking partner.
So, yep, it will definitely be coming with me on any future hike where either sunburn or spells of rain are a likelihood. I probably wouldn't bring it just on the off chance of rain, but then again, for 187g, it's not much of a burden.