They are still heavier than foam core floats, but the size and weight would work OK for your airplane.
A friend tried them and said they do not work well on the water, but I haven't tried them myself.
The best all around 40-60 size floats are the Falcon/Modelfly/Ready/Galleggianti floats, but I see that Hobby People (the latest importer) is not carrying them on their website any more. If you can find those, buy them.
These are also good floats on the water;
http://www.horizonhobby.com/Products...ProdID=SFM3814
Do NOT try to use Gee Bee Line floats. They are cheap for a reason.
Jim