We have two of them - one that I bought and one that I built. Do they work? - Yeah, more or less if it is a bright sunny day in the summer when the sun is up long enough to do the job. They work great for things like purifying water and making baked beans, less so for baking bread. Anything that is baked in a solar oven will not change color as it bakes. So a loaf of bread, although cooked, is still the color of the raw dough. They say you can paint on a little butter and it will turn brown. - Yeah, okay, sort-of; it's not the same.
The one I bought is the model from Solutions From Science. I bought it to have a pattern to make my own because I had never seen one in real life. Also, the reviews on it were considerably higher than some of the others. The first thing I noticed is the reviews lie. They claimed they were able to generate an internal temp of 400 degrees on a bright sunny day and claimed that it did not matter if it was winter or summer. That may be accurate if you live in Kenya and are testing it at high noon. The best I have been able to achieve with it was about 275 degrees in the summer. In the winter, it does not work worth a tinker's damn. Of course I live in Minnesota, so if I see the sun in the winter, it is usually well below zero.
Is it worth having? - Yeah, okay, maybe, I guess. They are big and bulky and take up a lot of storage space. They are slow to cook anything. The reviews claim a big benefit is that they do not give off any odor when you cook something in them. That is only partially true. The food you are cooking still gives off its normal cooking odor. But it is true there is no odor of a campfire.
At the end of the day, I would still prefer something like a rocket stove for cooking if I had to rely on it for survival. But as I said earlier, they do work pretty well to augment your Berkey for purifying water. So I would say put it on the "nice to have" prepper list, but still pretty close to the bottom of the list. There are a bunch of other things that work better.
