(there's a bug question after my long & wordy intro paragraph)
I tried Plato using the one click combo installer (Nickel Menu, KOReader, Plato),and it looks like a really nice alternative to the build-in reader -- VERY fast (I thought KOReader felt faster than the built in reader, but this was even faster!!), and very nice UI layout. While I don't think it'll be my first choice because I use a LOT of the features in KOReader, I think it'll be interesting to play with and maybe eventually recommend to users who want something fast, pretty, and easy to use, while having more functionality than the built-in reader, without being overwhelmed with every feature in the world!
Anyhow, one thing stops me from recommending it, and that is that all of my books in the main "Digital Editiions" library (all DRM free, side loaded or downloaded via Calibre OPDS in KOReader) will not open in Plato, they all show up as PNG files, even though they have either epub or kepub extensions and are readable in KOReader. They open, but it only shows the cover image and then says "no next page" if I try to move beyond that. The only book that I can read is one (the only one) in the CalibreWireless folder that I think was created by KORader.
EDIT: One other difference, is the books in the "Digital Editions" folder show up as filename, no metadata, and the one in the CalibreWireless folder shows up with metadata.