Yes, you are correct in that some swans have no idea about an island and may never use the floating object.

Swans have a lot of feathers (nature provided this protection for them with lots of down), so winter in and of itself is not going to be a problem. Swans are built for cold weather, but they also know when to get out (i.e., migration) and a pinioned bird cannot do this. So, shelter must be provided in that there is a windbreak and a food source nearby to supplement the lack of grass and other greenery. The food should be near the perimeter of the lake instead of the middle to avoid the birds from being caught in ice or frozen areas. However, this nearness to banks can attract predators, see below.

Blitz feeders work extremely well, but you will still need to check them to make sure that the food stays dry and does not mold. Usually, every 3-4 days is sufficient and will also alert you to how much food the birds are eating and if the food needs replenishing.

The major concern is the wildlife in the area. If food sources go scarce for the winter and swans are near banks and in open areas at night, the possibility that the swans will fall victim to prey is a real concern. Unless they go to the middle of the lake with a man-made island (big enough for them to sleep and walk around, then a predator situation is going to be the biggest concern.

Finally, there are photos and directions to placing the Blitz feeder in the water on this website. You will need to scroll down and search the questions, but we do provide a complete set of directions for installing and using the Blitz feeder. The Regal Swan