Thanks for this very good review. But I rather would say that Poseidon does not support *all* kinds of devices right now. There are always a bunch of evil mass storage devices, there are lots of cheap softmodems, dozends of old digital cameras, various scanners, new webcams, PDAs etc, which are not yet supported (and some never will).
However, I wouldn't say that Poseidon matches the AmigaOS3.x version, because it comes with PPC native binaries

The need to download two files will become obsolete with the next version, as there will be a special archive for the Pegasos aswell.