I have a GoSun sport model (smaller than the one pictured) and use it regularly on land. We like it overall, but it has it's plusses and minuses, and some of the disadvantages might be larger on a boat.
The GoSun products are based on evacuated glass tubes, clear on the outside and coated black and copper on the inside (for absorbtion and radiation of the light as heat). So they are by definition highly insulated, with just a tiny vent in the cooking tray to avoid steam pressure. This means they heat up fast in good sunshine and retain the heat, even after the sun goes away. Because of this design, they are likely the fastest and hottest solar cookers
on the market (I researched a few and read some of the DIY books). We have heated veggies in 20 minutes and cooked them in 45 minutes. But glass tubes are more fragile, especially on a boat, even if the reflectors fold up and protect the tube for storage
(in both the sport and grill
The built-in curved reflectors are easy to unfold and position correctly but a bit undersized, so they only have optimum heat in a narrow range of exposure. To get the speed and heat benefits from it, you really have to adjust it to the sun every 15 minutes. If you don't, it still cooks, just not as fast. The sport model has folding legs that are fine on land, but might need to be strapped down on a boat (or maybe wapped with some non-skid tape). It tilts in one direction, but it should be sitting on something flat in the other direction, which may be hard on a smaller boat. Maybe you would be able to create a mount for it, like a BBQ on a rail. However, they say not to leave it out without food cooking, so you'd need to make it removable.
In my opinion, the biggest limitation is the size. The Sport model cooks enough food for 2-3 platefuls, depending on how liquid it is. The food sits in a stainless steel
"trough" that slides into the tube. The trough isn't very deep, so soupy foods are probably out on a boat. Everything needs to be chopped or diced in the sport model, but the grill
model looks big enough for some cuts of meat (maybe a 1/2 chicken). You can bake breads and cakes, because the dough will firm up as it rises in the trough, but they won't be very large in the sport model. Loading the food into the trough and serving from it, not to mention cleaning
the long metal piece in a small sink is not as practical as a regular pot.
The link to the sailingtotem website shows the more traditional box cooker where you can cook in a regular black pot. That has the advantage of transferring to the stovetop if you don't get enough sun to finish cooking. With the box-type, you can also put the food in almost sealed jars, so you could do soups even at anchor
. On the other hand, the box-type have larger reflectors that might be a problem even in light breezes. I wish that blog article had shown the reflectors as well. Another difference is that the box-type is slower cooking, so you prep the food and sit it out for several hours (2-6). The GoSport type cooks faster (30-120 minutes) so you probably wouldn't want to leave it unattended (you can overcook things).
All in all, we enjoy using the GoSun sport, and it does make great tasting food. Even though it is not a slow cooker, it does heat the food from all sides through heat radiation, so I guess it cooks the food in its own juices. We like it enough that my wife is ready to buy their "Grill" model to cook larger meals
. Although from the link, I now see it is out of stock, so my wife won't get hers for Christmas